Bullet protrusion into the case

M

model14

Guest
Doyou think substantial bullet protrusion into the case below the neck effects accuracy? With the standard SAMI speck .260 chamber, the 6.5 SMK 142's protrude 3/16" below the case neck when seated just on the rifling (1/8" is boatail). With my starting load of 42 grns of H4350, there is room in the case for the bullet protrusion without compressing the powder (looks that way anyway). I will be shooting the rifle for the first time tomorrow, going through barrel break in.
 
My experience would indicate yes...

In my experience a bullet should not protrude beyond the shoulder of the case, and even better the bullet bearing surface should not beyond the neck soulder juncture. You also are going to find preasure issues develope with deep seated bullets.

Nat Lambeth
 
SmokeItIn said:
.. in my .25-06 I'm seating a Sierra GK SBT just below the neck/shoulder juncture by a small amount, maybe 1/8" off the top of my head. No pressure issues however I dont see a big problem with it as long as the bullet doesnt extend further to the shoulder/body juncture. I dont see how this could happening anyway..
Click to expand...

try some Barnes bullets, like the 30cal 180gr TTSX in something like a 300WSM loaded to fit a factory magazine to see some serious "hanging down in the powder chamber!"

al
 
model14 said:
Doyou think substantial bullet protrusion into the case below the neck effects accuracy? With the standard SAMI speck .260 chamber, the 6.5 SMK 142's protrude 3/16" below the case neck when seated just on the rifling (1/8" is boatail). With my starting load of 42 grns of H4350, there is room in the case for the bullet protrusion without compressing the powder (looks that way anyway). I will be shooting the rifle for the first time tomorrow, going through barrel break in.
Click to expand...

The SAAMI spec .260 Rem chambers have a very short throat so that a loaded round will fit into a Remington 700 short action magazine (nominally 2.800 inches) and still be somewhere close to the lands. That is just the way it is. It may not be "optimal", but the .260 Rem is capable of excellent accuracy. The 142 gr MK is a very commonly used bullet with the .260 Rem in high power rifle silhouette as well as other applications. Some people have long throated chambers which have more room for powder, but those are no long .260 Remington chambers.

Cutting to the chase, if you have decent brass and work up your load with the 142 gr MK, you should be able to achieve fine results.

Enjoy your .260 Remington. It is a fine cartridge.
 
Deep Seated Bullets

One other item to be wary of is to be sure there is no substantial "do-nut" at the neck shoulder junction. If there is, you will certainly feel it when you seat the bullet.

In todays Benchrest Game, shooters often fit the throat to a specific bullet design. It is little things like this that allow you to fine tune a set-up and get optimum performance.

Of course, unless you are involved in Competitive Benchrest, this is probably a non issue. But do keep in mind, the more the bullet has to be seated into the case, the less overall chamber volume you have.

In reality, to shoot the really long 6.5 bullets, you need enough freebore so that base of the boat tail is just about even with the case neck junction. But then, it might not go into the magazine.

Sort of makes you wonder why Remington doesn't build these chamberings on a long action............jackie
 
Extended Mag Boxes

Kevin Wyatt (Wyatt Outdoors) makes extended mag boxes for several makes of rifle, especially the Remington 700 and it's clones. They are available from a number of vendors Brownells, MidwayUSA are just two.

Nat Lambeth
 
Nat,

Wyatt mags are useful (I've had them on several rifles and recommend them), especially with VLD bullets, but still do not get the bottom of the bearing surface of most of the heavier 6.5mm bullets above the neck/shoulder junction of .260 Rem brass. Jerry Stiller offers them with his magazine actions if that gives you any clues. ;-)

As a "short action cartridge", the .260 Rem is just that way. The 6.5x47 Lapua keeps the bottom of the bearing surface of the 139 gr Scenar above the neck/shoulder juncture in the chamberings I have seen, and in mine.

Cheers.
 
Thanks all for very informative responses. I will consider this a non-issue for now and work on other areas to get my new .260 to shoot better.
 
Rick,
You may have read my other posts "silk purse from a sows ear". I started with a new $300 Rem 700 30-06 ADL with synthetic stock for 600 yard shooting. Through stock work (lots of lead and a BR forend), plus handloading the ammo, I was able to achieve 1 1/2 MOA, which was enough to not embaress me at the 600 yard shoots. Before I switched barrels,I was shooting Berger 185 BLD's into the 8 and above ring with consistency, but It was obvious it wasn't going to get any better without a barrel change. I had a local gunsmith (good reputation) install a 8.5 twist, 30", Bartlein barrel with .260 chambering amd in HV profile. The barrel is free floating with a good bedding job which includes 3" of the new barrel. The monster now weighs 22 pounds with scope. NO attempt was made to accurize the stock Rem 700 action (the gunsmith refuses to do it, says it is a waste of money). Besides, he felt the action was probably pretty good considering how the stock 30-06 barrel was shooting.

My first 50 rounds, using a standard barrel break in cleaning process and using a standard H4350 load behind SMK 142's has been very dissapointing. Fo all 50 rounds I seated 1/16" off of the lands. The chrono showed 2750 fps average, with fairly low spread. My best grouping for 5 shots has been about 1 moa, but most are scattered all over the target out to 2" or so.
This is a lot worse than the 30-06!

I have loaded up 50 more rounds with 10 at 1/16" jump, 10 at .030", 10 at .015", 10 at 0", and 10 at .010" buried into the rifleing. I will be testing these at the range tomorrow, with a thorough cleaning after every ten rounds. I sure hope this works out for me. All my bullet runouts are inside .004" inch so thats not an issue at this point.

To make matters worse, I have a stock Rem 700 VLS in .223 which I free floated ans bedded, and has a Rifle-basix trigger installed. It shoots 1/2 moa all day at 100/200 yards. I have less than $700 invested. I wanted to shoot 600 yards with HIgh Power, but my budget is under $1200, so that's why I wanted to do my own buildup. I was certainly expecting 1/2 moa from the .260, and it may yet be there with the right cartridge setup.
 
Model14
I don't shoot Sierra 142's but all of the Sierras I have shot like the bullets into the rifling or 0.020-0.025 off of the lands.I think your 1/16 off or 0.0645 is too much jump.If it was my gun I would seat them real hard into the lands and see how the groups look.
If the accuracy isn't there start backing them up in 0.005 increments until they shoot.
Waterboy
 
Try this...

I normally seat the heavier bullets about 0.010" off the lands in my 6.5-08s. My experience has been that "jamming" them in the lands usually results in pressure signs before I get to the velocity window I am interested in. Not "jamming" the bullet also means that you can extract a live round if you run out of time and not risk dumping powder in the action. (Some match directors can get touchy about being repeatedly asked permission to clear the rifle by fire.)

Take some of your loaded rounds and roll them on a flat surface. You should be able to see if any of them "not straight".

Back off your load to around 40 grains of H4350 and work up in increments of a few tenths of a grain. (Do this at a sorter distance such as 100 or 200 so that wind is less of a factor when evaluating the loads.) If you have some wind flags or can borrow some they will help reduce the effect of wind on your groups.

Take some Prussian Blue or even Marks-a-Lot and paint up the back of the lugs on your bolt and the work it a few times with a dummy cartridge to see if both lugs are engaging. Frankly, I am surprised at your 'smith not doing anything to the action. Most people will at least do a quick squaring of the face of the action and then lap the lugs. Running a modified bottom tap into the threads is even better to make sure that you will not be crushing the chamber with tapered threads from the factory.

If you are still experiencing problems, I would suggest getting a box of 6.5mm Sierra 120 gr MKs for testing, not shooting at 600. Load them with between 36.0 and 36.5 grains of either Varget or H4895 and seat them somewhere close to the lands. If this combination does not shoot, there is generally something wrong with the rifle.

Let us know how things work out.
 
Rick B said:
I normally seat the heavier bullets about 0.010" off the lands in my 6.5-08s. My experience has been that "jamming" them in the lands usually results in pressure signs before I get to the velocity window I am interested in.
Click to expand...

Rick are you saying that you have a chronograph and that bullets "jammed" will not achieve the same velocity as those "jumped?"

al
 
Yes

alinwa said:
Rick are you saying that you have a chronograph and that bullets "jammed" will not achieve the same velocity as those "jumped?"

al
Click to expand...

Al, I know that no less an authority than Walt Berger, with whom I have spoken about it, says VLD bullets must be jammed to achieve their full accuracy potential. That said, in my experience, using my reamers, with the powders I used, jumping bullets such as the 142 gr SMK, 141 gr Cauterucio or 130 gr Norma VLDs I have been able to achieve greater velocities jumping them a little bit rather than jamming them. So, yes, that is what I am saying. I have chronographed my loads over an Oehler 35p. I have also used the 139 gr Lapua Scenar with similar results.

The rifles in question were not bench rifles. They were silhouette rifles and the level of accuracy that is acceptable with them, for off-hand shooting, is not in the same league as a proper bench rifle. A 1/4 to 1/2 MOA rifle is considered quite good in that game and a 1/2 to 1 MOA rifle will frequently be considered "good enough".

I have not had access to an Oehler 43 to take a look at the pressure curve, but the signs I use to stop adding powder were as much the same as I could make them based on my experience.

Cheers
 
Good news!

Great news, it was the friggin scope!
A liitle background... I had a Nikon Monarch 6.5-20X 50mm I purchased new about 4 months ago. I tried to use it on my .223 but the zero was drifting badly with each shot. I sent it back to Nikon for repair, which they turned around fairly rapidly (1 week). Nikon never said they found anything wrong. I stupidly put this scope on my new .260 for the barrel break-in. Dumb! As I stated on my last post, I loaded up 50 more rounds with different seating depths and I put my old reliable Lyman scope on the rifle. Results were immediately good.
Here they are for 10 shot groups at 100 yards:

Seating (jump) Group size

.066 .861
.033 .736
.015 .736
0 .424
-.010 .861 (All horizontal spread, wind had really picked up and I didn't try to hold off)

All I had expected from this barrel change was 1/2 moa, and that is all I need to get a good start shooting 600 yards, which is all this rifle will be doing. Was the $550 expenditure worthwhile in going from 1 1/2 moa 30-06 to 1/2 moa .260. You betcha!!!!
Thanks for everyones input.
m14
 
Rick,

Look into getting a Hood Scope Checker.

Best money I ever spent.

By the way I have found that rings are at the heart of most scope problems. If you are not using precision rings lapped to the scope then you should try the Burris rings with the plastic inserts. They do make a difference!
 
Octopus said:
Rick,

Look into getting a Hood Scope Checker.

Best money I ever spent.

By the way I have found that rings are at the heart of most scope problems. If you are not using precision rings lapped to the scope then you should try the Burris rings with the plastic inserts. They do make a difference!
Click to expand...

I have not tried the Burris rings in a number of years. The ones I did try wound up in the trash. They had terrible machine work on the part that was supposed to mount on the Weaver rail and would not "stay put".

Are the recent ones better machined?

About the hood scope checker, a friend was to borrow one to check out a suspect scope. I will have to visit with him about it. Scopes are "high maintenance".
 
Rick B
The original Burris basis were so stiff you needed a very stout screwdriver to collapse the base enough to get them stable on your rail.I actually pinched mine by using a vise then opened them back up with a small screwdriver.

The newer ones are much better as the tensioning slot isn't full of metal.
Lynn aka Waterboy

P.S. Are you coming down for the NBRSA 1000 Yard Nationals in October?
 
Rick B said:
Al, I know that no less an authority than Walt Berger, with whom I have spoken about it, says VLD bullets must be jammed to achieve their full accuracy potential. That said, in my experience, using my reamers, with the powders I used, jumping bullets such as the 142 gr SMK, 141 gr Cauterucio or 130 gr Norma VLDs I have been able to achieve greater velocities jumping them a little bit rather than jamming them. So, yes, that is what I am saying. I have chronographed my loads over an Oehler 35p. I have also used the 139 gr Lapua Scenar with similar results.
Click to expand...

Al'righty then..... just making sure that I understood your experience.

al
 
I've tried to explain to owners of No.4 Enfield rifles converted to 7.62 Nato just why the British NRA put out a warning to not use either .308 or 7.62 ammo loaded with bullets weighing over 144 grains.

In that situation the converted Enfields were not proof tested for 7.62 ammo other than the Nato standardized ball ammo of 144-150 grains bullet weight.
When longer heavier bullets are used the limitations of OAL result in the base of the bullet protuding into the powder space, reducing effective case capacity.
If you look over the US Military technical specifications for the various loads in use by our own military you'll find that while Max Average chamber pressure of the M118 Long Range Special Ball is only 4K CUP higher than the 48,000 CUP of the M80 ball the Maximum Standard Deviation is 9,000+ CUP higher than the average pressure of M80 and 6,000 CUP higher than the Maximum Standard Deviation for M80 Ball.
It appears that as bullet weights go up theres not only an increase in average chamber pressure to maintain performance levels but also an increase in the percentage of deviation.
When bullets of 175 grain or higher are used with a No.4 rifle .308 loads that remain within the rifle's safety limits are no higher in velocity than comparable .303 loads which generate lower pressures than the same loads in a .308 case.

No one wanted to listen to my long winded warnings and now the Australian NRA has followed the lead of the British NRA in warning against use of loads using bullets of more than 144 grains.
There are vague recent reports of damaged bolts and blown out boltheads involving converted No.4 rifles. A bystander was injured when one rifle blew out its bolt head, which points up the fact that proceeding at one's own risk may also mean putting others at risk.
 
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