Trying different OAL again, what is giving me tight groups is 40.5 of IMR 4064 under a Sierra 168gr.HPBT with a .006 jam , brass headspace is .001 when looking at the numbers looks like jump is .005. Anyway I tried A-Max 168 boartails with same jam, recoil was a little more, group wasn't as tight. Lowered powder charge to 40.2 with a .012 jump, shot just as tight as the Sierra's. Next range trip will try Sierra with a .012 jump to see what happens. What works best for you? Distance is 200 yards.
What works best 4U jump or jam
- Thread starter cw308
- Start date
firewrench044
New member
Best guess is this is about a 308 with a 24" barrel
In all the Sierras and Hornadys I have tried, they all worked best between
10 to 15 off the lands
I did better using Varget with the 168s
I do use 4064 for the 175s
In all the Sierras and Hornadys I have tried, they all worked best between
10 to 15 off the lands
I did better using Varget with the 168s
I do use 4064 for the 175s
firewench044
Rem.700 308 cal. Barrel is a Rock Creek M24 5R 21" with a 11.25 twist I use it for bench rest shooting only. When I had it rebarreled I started AOL at 2.800, picked up the Hornady OAL length gauge, found 2.800 was a .006 jam but fired tight groups. Using Sierra 168's will give a test with a jump next time out. Thanks for getting back. Chris
44AMP, Yes. Jump is free distance from bullet ogive to lands. Jam is no distance, or how far into the lands the bullet is placed. Hope the info listed above will help in answering the question.
Rem.700 308 cal. Barrel is a Rock Creek M24 5R 21" with a 11.25 twist I use it for bench rest shooting only. When I had it rebarreled I started AOL at 2.800, picked up the Hornady OAL length gauge, found 2.800 was a .006 jam but fired tight groups. Using Sierra 168's will give a test with a jump next time out. Thanks for getting back. Chris
44AMP, Yes. Jump is free distance from bullet ogive to lands. Jam is no distance, or how far into the lands the bullet is placed. Hope the info listed above will help in answering the question.
I am the fan of the running start, I want my bullets to have that jump. I want the bullet to hit the rifling a-running. And then there has to be rational, if the bullet is setting at the rifling pressure forces the bullet into the rifling. If the bullet has that running start the bullet will be past the forcing cone and the beginning of the rifling before pressure gets serious.
But if I did stick the bullet into the rifling I would not be shooting max loads because there is that spike that is measured in time and pressure.
F. Guffey
But if I did stick the bullet into the rifling I would not be shooting max loads because there is that spike that is measured in time and pressure.
F. Guffey
If 2.800” was a .006” jam there is a chance if you chambered a round and then ejected it the bullet would remain ‘stuck’ in the rifling and or the bullet would be imprinted by the rifling. As you know we have to know the diameter of the rifling and most test tools are bullet friendly.
F. Guffey
Fotheringill
New member
I would suggest using the Berger method of finding the best for your particular rifle.
And I would think if the Berger method was worth mentioning it would be worthy of a link.
http://www.chuckhawks.com/developing_target_load.htm
I do not believe cw308 needs it but on the outside chance there are members following this thread they can become familiar Chuck Hawks and his methods and or techniques.
F. Guffey
What?
Shooting off a rest on a bench isn't bench rest shooting.
"...If 2.800” was a .006” jam..." 2.800" is the standard max OAL for a .308. OAL is measured from the pointy part of the bullet to the flat part of the cartridge, NOT the ogive.
If a 'jam' is the bullet sticking 6 thou into the rifling, it sounds like you have an unfinished barrel. A 2.800" OAL 168 grain bulleted cartridge should not come anywhere near the lands.
40.5 of IMR 4064 is a full grain under minimum. And brass does not have headspace.
Shooting off a rest on a bench isn't bench rest shooting.
"...If 2.800” was a .006” jam..." 2.800" is the standard max OAL for a .308. OAL is measured from the pointy part of the bullet to the flat part of the cartridge, NOT the ogive.
If a 'jam' is the bullet sticking 6 thou into the rifling, it sounds like you have an unfinished barrel. A 2.800" OAL 168 grain bulleted cartridge should not come anywhere near the lands.
40.5 of IMR 4064 is a full grain under minimum. And brass does not have headspace.
F. Guffey, thanks again. Haven't had the problem with a bullet held in by the rifling, we get a 5 minute working at the range, this when I fire my last round. I check my OAL with the RCBS precision mic, made a mistake with the mic was 360 degree out mistake, making the new bullet I was trying A-Max 168 gr. BT 50 thousands longer. Talk about a jam, had to use a rubber mallet on the bolt handle to remove the round, felt like such an AH. First time for everything. I do like the idea of a jump even with a mild load. Starting with my next reloads.
mikld, it sounds worse then it sounds. Not really jammed into the rifling, if case neck hold is light the bullet will remain in the barrel dumping powder into the action, its that time when you hear curse words never used before. Some bench rest reloaders soft seat there rounds,with a very light neck grip, never tried it though& don't want to.
Fotheringill, Your not shooting on Sundays anymore. Al was there this past Sunday. Still fire formng, neck sizing. I'm looking into finding a round with a jump. How is your Savage benchrest 223 coming along. Be Well Chris.
mikld, it sounds worse then it sounds. Not really jammed into the rifling, if case neck hold is light the bullet will remain in the barrel dumping powder into the action, its that time when you hear curse words never used before. Some bench rest reloaders soft seat there rounds,with a very light neck grip, never tried it though& don't want to.
Fotheringill, Your not shooting on Sundays anymore. Al was there this past Sunday. Still fire formng, neck sizing. I'm looking into finding a round with a jump. How is your Savage benchrest 223 coming along. Be Well Chris.
603Country
New member
I'm with F Guffey. I load off the lands. Distance varies with the rifle. If loading the bullet into the lands will help me shoot a tiny bit better, it's likely I'll never see the improvement. And I'm a pretty darn good shot and have good equipment.
T.O' Heir
I know how to measure the ogive with a RCBS Precision Mic & the AOL with a caliper. When I size my cases from shoulder to bolt face, I have .001 free space measured with a mic. I call it headspace. If I'm wrong, big deal. What would you call it?
When I had the rifle rebarreled, talking to the gunsmith, telling him the rifle would be used or benchrest only & the bullet I would be shooting most of the time also the distance & on the low side of a charge. Could be the reason I have no jump at 2.800 if measured a caliper. I do all my measurements with a mic.
Now back to the question. Do you jump or jam your rounds for accuracy.
I know how to measure the ogive with a RCBS Precision Mic & the AOL with a caliper. When I size my cases from shoulder to bolt face, I have .001 free space measured with a mic. I call it headspace. If I'm wrong, big deal. What would you call it?
When I had the rifle rebarreled, talking to the gunsmith, telling him the rifle would be used or benchrest only & the bullet I would be shooting most of the time also the distance & on the low side of a charge. Could be the reason I have no jump at 2.800 if measured a caliper. I do all my measurements with a mic.
Now back to the question. Do you jump or jam your rounds for accuracy.
603Country
I'm with F Guffey also. Didn't like the idea of a jam, being I am loading on the low side with no pressure problems & shooting tight groups, l left it there. Once I tried the A- Max 168 measured a round from a range friend using store bought match A-Max rounds. With a caliper AOL 2.800 But mic setting to the ogive gave me a . 012 jump, tried the setting , shot just as accurate. Now I will try the Sierra's with a jump this Sunday.
I'm with F Guffey also. Didn't like the idea of a jam, being I am loading on the low side with no pressure problems & shooting tight groups, l left it there. Once I tried the A- Max 168 measured a round from a range friend using store bought match A-Max rounds. With a caliper AOL 2.800 But mic setting to the ogive gave me a . 012 jump, tried the setting , shot just as accurate. Now I will try the Sierra's with a jump this Sunday.
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Brian Pfleuger
Moderator Emeritus
I have personally decided that trying to "touch" the rifling takes entirely too much effort for my needs.
I once thought that a bullet would touch the rifling and that would be it, like a brick wall. There would be too much resistance and too little force to go any farther, I underestimated that rather gradual introduction of the rifling and the force of the camming action of a bolt or even just closing action on something like an Encore.
For a while, I toyed around with various "touching", "jammed" and something in between lengths.
Then I pondered the differences between those lengths, often just a few thousandths, my own ability to reliably find them *exactly* and the variation in my own loaded ammo... hm.
I now conclude, for almost all my rounds, that I will find approximately "touching", back it off 0.05" and shoot 'em.
Every gun I load for shoots very well when I do that, some under 1/2", some closer to 1" but plenty good enough even for killing woodchucks waaaaaay out there.
Any more effort just isn't worth the return.
I once thought that a bullet would touch the rifling and that would be it, like a brick wall. There would be too much resistance and too little force to go any farther, I underestimated that rather gradual introduction of the rifling and the force of the camming action of a bolt or even just closing action on something like an Encore.
For a while, I toyed around with various "touching", "jammed" and something in between lengths.
Then I pondered the differences between those lengths, often just a few thousandths, my own ability to reliably find them *exactly* and the variation in my own loaded ammo... hm.
I now conclude, for almost all my rounds, that I will find approximately "touching", back it off 0.05" and shoot 'em.
Every gun I load for shoots very well when I do that, some under 1/2", some closer to 1" but plenty good enough even for killing woodchucks waaaaaay out there.
Any more effort just isn't worth the return.
603Country
I'm with F Guffey also. Didn't like the idea of a jam, being I am loading on the low side with no pressure problems & shooting tight groups, l left it there. Once I tried the A- Max 168 measured a round from a range friend using store bought match A-Max rounds. With a caliper AOL 2.800 But mic setting to the ogive gave me a . 012 jump tried the setting shot just as accurate. Now I will try the Sierra's with a jump this Sunday.
I'm with F Guffey also. Didn't like the idea of a jam, being I am loading on the low side with no pressure problems & shooting tight groups, l left it there. Once I tried the A- Max 168 measured a round from a range friend using store bought match A-Max rounds. With a caliper AOL 2.800 But mic setting to the ogive gave me a . 012 jump tried the setting shot just as accurate. Now I will try the Sierra's with a jump this Sunday.