30 br??

N

Nor Cal Mikie

Active member
Thinking about building a 30 BR and have a few questions.
Knowing in advance that all rigs don't work the same, for you guys that are shooting the 30 BR, when chambering a barrel,where are you setting your bullets. Jam or Jump? I'am thinking about starting with the lightest bullets available and the shortest freebore so I can jam or jump as needed or desired. Opinions and input appreciated. Thanks, Mike.
 
I started with them just kissing. It's 2000 rounds later, and I have not checked it recently. Still shooting the same depth on my seater die. Shot the smallest group ever 2 months ago.
 
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Mike....you really need to decide which bullet you want to shoot...there are many good 30 caliber bullets out there...the 7 ogive bullets made on a .940" jacket will have plenty of freebore at .025"...but if you choose a 9-10 ogive bullet on a 1.00" jacket you will need a longer freebore...talk to Dave Kiff at PTG and he will tell you what is popular...
I don't recommend a "zero" freebore due to my (bad) experience with it...jump or jam will be dependent on what your barrel likes...I do well with a .025" freebore using a 7 ogive 112 grain bullet on a .940" jacket...just kissing the lands...loaded to 3015 fps...neck tension is important...you will need several bushings to find which will give you the best accuracy...the easiest way to get great brass (critical) is have Ron Hoehn make it for you..!

Eddie in Texas
 
There are probably exceptions but most barrels like a bullet seat length of kiss to some jam and a fair amount of neck tension.
 
I'm confused.......
Isn't freebore or jump the same thing?
If so, seating depth would establish freebore with any ogive (?).
How does a reamer create freebore...longer neck area?
I guess you can tell I'm new to this. LOL
 
Freebore is set by the reamer cut. And can't be changed without recutting the chamber with a shorter or longer length throat reamer.
Jump or jam is where you set the OAL of your rounds in relation to the starting of the lands. Some folks like to jam the bullets into the lands. Some folks like to jump the bullets to the lands. Each rig is different so you have to try each way (jump or jam) and see what works best. And the bullet you choose will depend on how long the throat is. Short bullets may end up with little neck contact if the throat is too long and you try to jam them into the lands. I prefer as much neck contact as I can get. The throat will only get longer as more rounds are fired. Longer throat will let you shoot longer bullets (and still have lots of bullet in the neck) as the throat wears, and it will.;)
 
Thanks for the explanation, Mikie. Would a zero freebore cut have the max case length right at the lands and not allow any jump? Jump could only be achieved by reducing case OAL with neck trimming?
 
Without looking at a reamer print, I'am not sure. Seems that there is a slight distance between the end of the case neck and where the lands start. Some of the guys here are a "lot" more informed than I am.
Changing the OAL of the case won't effect the acutal cut of the reamer. It's set when the chamber is cut. The distance from where the end of the case neck is to where the lands start is the freebore. Like I said, I prefer my bullets set as deep as I can get them in the case neck. Not really sure if that's the best way but it works for me. And as you fire more rounds, the freebore gets longer and pretty soon you can't shoot the lighter bullets and still have a bunch of bullet in the neck and reach the lands to to a jam. So you make your choice as far as how much freebore you want for the bullet you plan to start off with. As the throat gets longer you can go to a heavier bullet to reach the lands and still have a bunch in the case neck.
My guess is that a lot of the guys will scrap their barrels as the throat gets longer and they can seat their bullets where they want them? Things are a little different when you're shooting Compitition then shooting varmints.
 
fishbone said:
Thanks for the explanation, Mikie. Would a zero freebore cut have the max case length right at the lands and not allow any jump? Jump could only be achieved by reducing case OAL with neck trimming?
Click to expand...

I have probably had Eight 30BR barrels at this point , never had one yet that liked to be jumped! They like lots of neck tension and seem to respond best to being buried hard in the lands, I wish it were not so as buried hard in the lands can be a problem if you try to eject an unfired round. I have had some that worked fairly well with it just kissing the lands but none that liked jump.

Dick
 
freebore is a bullet diamater section of barrel from the case neck to the leade, the leade is a tapered section of the lands to ease the bullet into the lands. therefore even with zero freebore you will still have to seat the bullet out to engage the lands. Jam is the bullet seated as far into the lands as it will go, in other words let the bolt seat the bullet start there when trying to find seating depth and back off of jam until you find the place it wants to shoot
 
Got it. Freebore is the distance from where the bore starts to where the lands start. A reamer, therefore, cuts the chamber, the neck area and into the bore to create a section of freebore.
Sorry to screw up Nor Cal Mikie's thread.
 
Screw up my thread? Never happen! We're in it to learn all we can and every bit of "been there, done that" is what makes these guys good teachers. If it wasn't for some of the information we pick up here and other places, I'd be fumbeling in the dark. Thanks Guys, Mike.
 
30BR baseline

This is where I start whenever I work with a new 30BR barrel. Even if you tweak a bit from here, this gets you in the ball park right away.

Assuming a well built gun done with a known good reamer of common 30BR specs. (.330-ish neck), a quality BR grade barrel twisted 16-18 and BR grade bullets (BIB, Euber, 10X, Cheek, etc) of 112-125 gr. weight on .925" or 1.00" jackets:

-Neck clearance of .002 minimum as measured over the pressure ring
-Neck bushing .004 smaller than the neck measures over the p.r. (see above)
-Fed 205M or WSR primers
-Seating stem set to 'jam' .020-.025
-H4198 Extreme starting @ 32.0 and go up in .5 gr. increments

With this, any well built gun will show you at least two...maybe three...accuracy nodes from down low until you can't get any more powder in the case...which is typically around 34.8-35.0 gr. of H4198 Extreme. Understand that H4198 is borderline too slow in the 30BR case and often better results are achieved in the upper load areas or by picking up the bullet weight and/or bearing surface length as a tuning aid to increase pressure.

After you find the node that shoots best, the next step is to back off the seating depth in .005 increments looking for any improvement. When you've settled on that, you might try decreasing the neck tension in .001 increments.

For what it's worth..... -Al
 
My best 30BR barrel to date really didn't seem to "care" much about powder quantity. Did a test one day and loaded several batches with .5 grain load variations and then shot test groups. The group location moved around the target but there was no meaningful change to group size. If I remember correctly, from my base load I tried +1 to -2.5 grain variation in the test. After years of dealing with quirky 6 PPC's, I thought it was great.
 
Nor Cal Mikie said:
Thinking about building a 30 BR and have a few questions.
Knowing in advance that all rigs don't work the same, for you guys that are shooting the 30 BR, when chambering a barrel,where are you setting your bullets. Jam or Jump? I'am thinking about starting with the lightest bullets available and the shortest freebore so I can jam or jump as needed or desired. Opinions and input appreciated. Thanks, Mike.
Click to expand...

Zero freebore will shoot a good variety of bullets and allow you to experiment with bullet seating. Almost everyone I know has success with a decent jam.

Mike
 
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Nor Cal Mikie said:
Screw up my thread? Never happen! We're in it to learn all we can and every bit of "been there, done that" is what makes these guys good teachers. If it wasn't for some of the information we pick up here and other places, I'd be fumbeling in the dark. Thanks Guys, Mike.
Click to expand...

Absolutely spot on there Mike;)
Wayne.
 
eww1350 said:
Mike....you really need to decide which bullet you want to shoot...there are many good 30 caliber bullets out there...the 7 ogive bullets made on a .940" jacket will have plenty of freebore at .025"...but if you choose a 9-10 ogive bullet on a 1.00" jacket you will need a longer freebore...talk to Dave Kiff at PTG and he will tell you what is popular...
I don't recommend a "zero" freebore due to my (bad) experience with it...jump or jam will be dependent on what your barrel likes...I do well with a .025" freebore using a 7 ogive 112 grain bullet on a .940" jacket...just kissing the lands...loaded to 3015 fps...neck tension is important...you will need several bushings to find which will give you the best accuracy...the easiest way to get great brass (critical) is have Ron Hoehn make it for you..!

Eddie in Texas
Click to expand...

The quote (in red) is incorrect: the bearing (shank) length on 9-10 caliber (tangent) ogive bullets, based upon the 1.00" long jacket, will be very similar to the bearing length of 7 ogive bullets which are based upon .925" jackets. With ZERO freebore, and a 1.5 degree throat angle (3.0 deg included), and the bullet 'kissing' the lands, the bases of all of the configurations (above) will be roughly 1/2 way into the case-neck. For a thrity caliber BR rig, unless you plan on shooting the more blunt ogives 7/8, based upon the 1.00" long, or longer, jacket lengths, freebore (especially more than 0.030") is a bad idea.

Too long a chamber - relative to potential case/neck length simply makes for counterfeit freebore, and is VERY bad medicine: a chamber cut to accommodate a .350" long neck, 'filled' with a case featuring only a .320" long neck, and .030" of [real] freebore, is a recipe for frustration: a poor equivalent of .060" freebore, 1/2 of which is NECK diameter! :p Make certain that your case forming methodology and chamber reamer make for compatible neck/overall [case] length.

Also, if freebore is desired, getting a reamer with too small a freebore diameter is a bad deal: the freebore diameter must remove every last vestige of the lands, and 'clean-up' the groove! A tighter (than .3085") freebore diameter is undesirable. A thirty caliber reamer should NEVER cut less than a .3085" diameter freebore . . . and up to 0.3090 works quite well. Keep 'em ON the X! RG
 
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