Rear Locking actions?

[Ackley Improved]

Guys... For my own curiousity... why have no big name custom action makers made rear locking lug BR actions?

What are the negatives/positives for them?

I mean I will not swap my BAT for anything, just curious!

Cheers

 

[K Battenbough]

I believe that a rear locking lug bolt will flex more than a conventional front locking lug bolt.

KB

 

[Larry Elliott]

Under 60+kpsi pressures common in BR loads steel compresses more than many people consider likely. I'm not an engineer, but if the compression is say 0.001"/inch at 60+kpsi which I think is maybe a conservative guess and the locking lugs are 4 or so inches behind the bolt face that's 4+ thousandths of bolt compression that wouldn't be found in a front locking action. The bolt and fired case will try to return to their original dimensions, but bolt opening will be very stiff and case life will be reduced considerably. With a front locking action there's only maybe an inch of steel from the bolt face to the rear of the locking lugs so compression would be much less.

For "normal" pressures in factory ammunition, and if the cases aren't expected to be reloaded rear locking lugs are not a problem. But let someone fire a hot load or try to reload fired cases very many times and there will be case failures and/or rejections due to incipient head separations.

 

[Dennis Sorensen]

Guys... For my own curiousity... why have no big name custom action makers made rear locking lug BR actions?

What are the negatives/positives for them?

I mean I will not swap my BAT for anything, just curious!

Cheers

My thoughts...
Rear locking lug actions will not handle the pressures as well as a front locking lug action... If they made one heavy enough it may come close but it would be a considerably overweight action...

 

[Flouncer]

Law .303 British

I think you just diagnosed - described the Enfield or SMLE action. And the cases are reputed to be stretched after only a few firings.

 

[alinwa]

Also the 788, a fine and accurate action for moderate loading but a real loser when the pressure climbs.

The term I've heard used is "bolt compression."

it's real

al

 

[Stephen Perry]

Rem 788

Every action has a pressure limit, when exceeded trouble occurs. The 788 action functions perfectly within it's it's pressure limits. I have a 6x47 BR gun using a 788 action Hart barrel that shoots fine with a caseful of 748.

Stephen Perry
Angeles BR

 

[alinwa]

AI, you may already be familiar with the Inch action being made in Australia http://actionclear.com.au/ it is a rear locking desing. I've examined early prototypes and corresponded at length with the designer, Robert Chombart and the manufacturer, it appears to be a very solid design, in every sense of the word.

I hope to have a production version at some point this year to do a complete write-up on.

Hey German,

I'd read a small report on the Inch and recently read over the website info. Looks to be really solid. And heavy?

I'm just guessing.

I tend to think in terms of 10-10.5lb weight limits.

al

 

[GerryM]

Rear locking action

I also have a 788 action. And your correct.
It also has a shorter lock time then a 700 or 600 series.
It's a 222 and shoots light out at 100 yds.
I haven't ever seen the bolt flex after barreling it several times.
Once in a 6/47 , the 222 mag the 222.5 and back to the duce.

 

[R.G.C]

Al, looking at my notes, I see that the prototype I handled weighed 2 lb, 14.5 oz. (46.5 oz.) with the trigger in place. In fullbore shooting, we hang relatively heavy 30" barrels from the action so a fair amount of mass is a good thing both for rigidity and balance. Of course, the same design can be made lighter and smaller or even in a different way altogether if light weight is an objective.

While we prone shooters don't value fast bolt cycling too much, for instance; I am aware that Benchrest shooters place a higher value on it. A rear lug action will have a slightly shorter bolt throw for a given amount of loading port exposure and with no lug abutments to interrupt the feeding process, it can be made to feed very smoothly.

In its present receiver body, the Inch isn't going to be a Light Varmint class contender, it's too heavy. That's not to say the same rear lug bolt couldn't be housed differently for such purposes. However, it would make a very good 600 - 1000 yard Benchrest action in its present form.

Each design has it's strong points, the rear lug design is a short(er) throw, fast feeding design, with excellent gas containment. The Inch appears to overcome the design's traditional rigidity and bolt flex problems and the trigger is the superb X-Treme Trigger design. I'm eager to hold a production version in my hands and to report on it.

Thanks, German, for your appreciation.

New to this forum, Regards to all members from Normandy.

The question of case stretching came from the SMLE, having a thin sectionned bolt and two lugs positioned vertically when closed (co,trary to al other 2 Lugs designs), the bottom one bearing against a solid surfacee, and the other on a bridge. This action was as flexible (but not souding same) as a tuning fork…

Other designs, the Schultz and Larsen M62 and the Steyr-Mannlicher SSG and hunters for instance, does not have this problem.

The possible compression of a generously dimensioned bolt is a MYTH. On the INCH, the smallest cross section of the bolt amounts for 310 square millimetre. The value to use is the elastic isostatic Modulus, for you Americans, the Bulk Modulus. For the steel and treatment used for both Bolt and Receiver, it amounts at 170Gpa, or 170 kgs/mm2. In other words, for the smallest cross section of the Bolt, the total reesistance before flexion occur is 310 x 170, or some 53 metric tons!!… Even shooting the .338 Lapua Magnum case never showed any problem.

Points to consider:
-The case head is totally surrounded by cylinders, no irregular shape as in front locking. The Bolt is centered in the Receiver directly at front level of the casehead, not almost 1 inch behind as in front lockings.
-Cone breech for feeding.
-The reduction in bolt travel amounts 25%. German consider this is not important for prone shooting, but users consider it is a plus, as there is no interference with the Cheekpiece, who can be extended forward accordingly for a better comfort.

I am not going to bore members praising the system, but am ready to reply to any question…

Sincerely
R.G.C

 

[alinwa]

This action was as flexible (but not souding same) as a tuning fork…

LOL!



al

 

[woody_rod]

Hello all,

Also my first post here. These forums are a great way to learn stuff for shooters, and also ask makers and suppliers to provide information, and correct and misconceptions.

Thanks very much to German, whom I have communicated with now for over 3 years. Geram is one of those rare people that is approachable, knowledgeable and OBJECTIVE. The last attribute is an extremely rare occurrence these days.

I am the guy that actually makes the INCH actions, so with Robert the designer, we can answer any questions anyone might have. Along with my business partner, Chris, we operate our business from a rural location in the lower West corner of Western Australia.

 

[woody_rod]

Also the 788, a fine and accurate action for moderate loading but a real loser when the pressure climbs.

The term I've heard used is "bolt compression."

it's real

al

Sure its real, but only in long distant past action designs.

The INCH is not really designed for BR work, I have to add in the beginning, but I doubt very much that any current action will have the same ultimate strength. There is no case stretching at all. From the 3000+ rounds I have shot through the INCH, not one has ever shown signs of stretching, other than typical brass flow from use.

The only thing real about case stretching in the case of the INCH, is that people have the opinion that it is real. In fact, as Robert says, it is a MYTH.

The INCH is made for disciplines like Palma and UK Match Rifle, where in the latter they use very hot loads to drive heavy (like 200 grain) bullets to 1200 yards, using only the standard 308 case. The case size the the barrel weight limit of 2,5 kilos (5.5 pounds) are the only limitations.

The INCH action looks like this: (This one mounted in a NZ made Millenium stock.)

There are now new designs coming other than the INCH, and also variants of the INCH, such as the F.INCH which looks like this: (viewed from the left side, showing the loading port, the longer ejection port is not shown on the other side)

This is a dual port, ejector model of the INCH, made specifically for prone scoped rifle type events like the Australian F Class, and also US and UK F/TR. The body weighs 900 grams, or around 2 pounds. They are made to handle the weight of massive barrels, cycle fast, and maintain excellent accuracy. This one is my own production unit, and the highly polished exterior will be PVD coated in Titanium Nitride, giving a very bright gold colour.

 

[alinwa]

Woody_rod, I believe you

I'm not in any way arguing any deficiency of the Inch, it looks and sounds like a bruiser. But the 788 isn't well suited for BR pressure loading. And that specific question comes up quite often.

al

 

[Tony Z]

Trev, you wanted some opinions.............
Compression of the bolt, for some reason seems to be the one area many people seem to drift to when it comes to rear locking actions. This is not the problem these sorts of actions have. The reason that the Rem 788 is prone to pressure increases causing subsequent stiffer bolt lift sooner than in a conventional front locker, is not from the compression of the bolt, but from the stretch of the action and the flex at the port cutouts. Wherever you have a cutout and have pressure applied, the pressure force is going to flex the action, and in the case of the 788 with all its cutouts and slender rails left to do the work, they stretch. The old Enfields are an extreme example of this stretch and are well known for case separations and action lockups.
I will guarantee with absolute certainty that on firing a cartridge that produces 60,000+ psi, a rear locking action flexes at the ejection port and at every other port forward of the locking lugs. A front locking action will also move on the same 60,000 psi, but the actual action length the pressure is acting on is not the same cumulative length it is with a rear locker, so it will take more pressure to get the bolt lift to become stiffer.

No matter which way you word it, steels compress, they elongate and they flex at the weakest point. Symmetry in this case would be beneficial, but you will never escape these properties. The only way to limit these properties is to make things bigger in the critical areas, and in the case of actions, this means more weight that may exclude them from certain shooting classes.
As for accuracy? Well some say the 788 was so accurate from the box because of its rear locking action. My money is on the longer tenon and total spring and firing pin clearance inside the bolt sleeve as well as the square sears that delivered repeatable ignition.

 

[goodi]

rear locking actions

rod

approximate scaling and measuring from :-

http://www.actionclear.com.au/docs/6-2,FIRINGPINASSEMBLY.pdf

appears to indicate that if the bolt outside diameter is 22mm ,then the maximum internal bolt recess diameter is approx 13mm.

minimum cross sectional area of bolt body would therefore be around 246 -247 sq.mm.

are these dimensions and X sectional area close to the actual sizes of the bolt ?

cheers
goodi

 

[R.G.C]

Trev, you wanted some opinions.............
Compression of the bolt, for some reason seems to be the one area many people seem to drift to when it comes to rear locking actions. This is not the problem these sorts of actions have. The reason that the Rem 788 is prone to pressure increases causing subsequent stiffer bolt lift sooner than in a conventional front locker, is not from the compression of the bolt, but from the stretch of the action and the flex at the port cutouts. Wherever you have a cutout and have pressure applied, the pressure force is going to flex the action, and in the case of the 788 with all its cutouts and slender rails left to do the work, they stretch. The old Enfields are an extreme example of this stretch and are well known for case separations and action lockups.
I will guarantee with absolute certainty that on firing a cartridge that produces 60,000+ psi, a rear locking action flexes at the ejection port and at every other port forward of the locking lugs. A front locking action will also move on the same 60,000 psi, but the actual action length the pressure is acting on is not the same cumulative length it is with a rear locker, so it will take more pressure to get the bolt lift to become stiffer.

No matter which way you word it, steels compress, they elongate and they flex at the weakest point. Symmetry in this case would be beneficial, but you will never escape these properties. The only way to limit these properties is to make things bigger in the critical areas, and in the case of actions, this means more weight that may exclude them from certain shooting classes.
As for accuracy? Well some say the 788 was so accurate from the box because of its rear locking action. My money is on the longer tenon and total spring and firing pin clearance inside the bolt sleeve as well as the square sears that delivered repeatable ignition.

Tony,
Up to the bulk modulus corresponding to its specifications and treatments, steels does not change form under compression. ‘Buckling’ happens on excessive loads. In the case of a hollow plain cylinder, it takes the form of either an inflation or ‘bellying’ (hope the term is correct?) or, if not maintained, bows….

When a solid such a thick walled tube like a bolt of those dimensions is maintained in a close toleranced bore with the minimal of openings, it cannot ‘belly’ or bow, and remain in perfect dimensions. As there is no change of form radially, there is then no more change (shortening) axially.

But steel elongates under high traction and ossible elongation of too minimal dimensionned external holding element (the receiver), or if flexible as for the “Smellies”, or with too small cross sections at points of the periphery (generous loading ports and magazine wells allow this cylinder to extend and not in an even symetric fashion, as extension is greater where the section are minimal…

R.G.C

 

[R.G.C]

rod

approximate scaling and measuring from :-

http://www.actionclear.com.au/docs/6-2,FIRINGPINASSEMBLY.pdf

appears to indicate that if the bolt outside diameter is 22mm ,then the maximum internal bolt recess diameter is approx 13mm.

minimum cross sectional area of bolt body would therefore be around 246 -247 sq.mm.

are these dimensions and X sectional area close to the actual sizes of the bolt ?

cheers
goodi

Goodi,

Tbe bolt is bored in steps, the bigger bore diameter being behind the lugs..

The mid section indicated is taken where an eventual buckling could happen, and this is at the level of the ejection port, the bolt diameter being totally encircled by the receiver crossection in full at front of the bolt, and at rear from well ahead of the locking lugs to well behind them. The ejection port takes approximately 60° of the circumference only.

When calculating for buckling, one takes usually the “eventual’’ flexion at middle of unsupported points, hence the indication of this section at near middle of ejection port level.

R.G.C

 

[Stephen Perry]

Rem 788 & Weatherby

Alinwa you write some good stuff but like me from time to time you tend to generaliize. The issue of the rear locking lug action has come up several times before, the Rem 788 getting the most attention. Al where are you getting your info that a 788 will not handle BR pressures and what do you consider BR pressures. Let me say some of you guys seem fascinated with this upper window loading. You don't need upper window or what some would call 55,000+ psi loads to shoot well in BR. Like I said earlier I have a 788 that I used in the past to shoot BR. My 788 when I shoot it is loaded the same as any 6x47 of it's time including my xp100 action 6x47 BR rifle. So the myth that a 788 will not take BR presseure is a myth. My 788 shoots well, action functions as it should, and brass loads as expected no more stretching than any of my Hall, Wichita, or Remington 40x/600 actions I use. The 788 is one of the strongest actions ever built so the flexing is not an issue, not my opinion alone. This Post is not promoting the 788 as a BR action just clearing up some of the myths of a good action.

The rear bolt of the the 788 with it's 9 locking lugs has been commented on before. any smith will tell you that you will never get all 9 locking lugs to engage at the same time. Remington never intended for this to happen. On my 6x47 the smith that built the gun has 3 lugs engaging in a longitudal row. I assume the other 6 lugs make contact with the reciever lugs when the gun is fired but the contact will not show on the lugs. What I see is the lapping the smith did to get the 3 to close on the reciever lug together. I have a 788 in .223 that shows little if any contact on the lugs, this is a factory gun.

Weatherby has used a front locking lug bolt that has 9 locking lugs and I would say they don't get all 9 lugs to engage together either. I was always taught the 788/Weatherby type bolts using the 9 lugs where each lug takes part of the pressure from the fired round as a safety issue. Actually with the 788 most that own them know that it's an accuracy system that works.

The inch action looks acceptable to me. Besides the myths that only a front lug action will will perform I'd like to see inch on a BR rifle. Make for some good conversation.

Stephen Perry
Angeles BR

 

[GerryM]

Rear locking actions

I'm not familiar with the syle action you fellows are talking about. But i'm willing to learn I understand you senario about the bolt flex theory.
Let me just say this. Many 788 actions only hit and some of the lugs at the rear. My action lugs are lapped , so all 9 hit . The 788 bolt lift was a plus also along with the quick lock time.
I enjoyed the action for many years , Actually it was my first bench rig.
I shot many small groups with it and had few problems. Case sizing was normal . Of course i was shooting a 222 , {but not at recomended loads.
Actually 1 to 1. 5 grs over max. I believe the loads were above the 50,000 \ lb pressure limit of the advertized pressures/
I can only say this how much pressure is enough? I believe 55,000 is quite adequate. Most cases today shoot at those pressure ranges at the factory and on the balistic tables. After a while we hit a point of no return on our loads. {thats were we add more powder to the loads and get less velocity. I didn't belive it until i started increasing over the chronograph.
I like the short lock times associated with the rear lock up and a possable 60 degree bolt lift, The worst part about the 788 was the cheezy bolt handle. Of course that was fixable.
I may seem like ancient history with this action but i must say several matches were won on this action. Jerry hart did very well with on in benchrest for a few years.
Built properly i think it would be a fine action to use.
But Thats just my opinion.
I'm glad to see the rear lug concept being tried again.
The smooth rapid bolt throw is a great asset. especially when time is a consideration. Keep us posed as to results in the coming matches it quite interesting to me. I'm sure others may also like to see the results
The new thing in benchrest is speed shooting. Maybe this is one aproach.
Keep up the good work on new and exciting actions..