7x57mm - Searching for Seat Depth
- Thread starter Rookie21
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If you are talking to me, I shoot nothing less than 10 shots with ample barrel cooling time, since almost all my rifles are for hunting. I do not shoot competition any longer, but did shoot a lot of silhouette in the 70s. That was my efforts at competition.
If you are talking to the OP, my answer is "I don't know" and apologize for buttin' in.
Land chasing is difficult. There used to be a page up by a fellow who spoke with a Somchem guy from way back when they had a load development program people could sign up for and bring in their rifle. They developed the charge with the bullet contacting the lands because that makes pressure about 20% higher than when it is 0.030" off the lands. You never want to take a max load developed well off the lands and just move the bullet out into land contact. It takes about 10% less powder to hit the same pressure when in contact with the lands. Anyway, the story related was that a fellow brought an old 8 mm Mauser to the load development service. Inspection showed the throat was badly worn, but the owner said it was his grandfather's hunting rifle and he wanted to be able to hunt with it again for sentimental reasons. So, they proceeded to try. The furthest forward load wasn't promising, so they set the bullet deeper in and it shot better. And they kept backing it in deeper and it kept getting better. In the end, it shot a group of about 1/4", IIRC, and was the most precise shooting hunting rifle and load the program had ever produced.
The late Dan Hacket told of a 40X chambered in 220 Swift he had for benchrest shooting that only grouped 5 shots into about 1/2 moa no matter what bullet and load he used. He always seated 0.020" off the lands because everyone said it tended to be best and he'd had good luck with it in the past. Then one day in changing to a bullet that was 0.015 shorter than the one he had been loading, he turned his seating die micrometer the wrong way, so instead of letting it come forward 0.015 he wound up adding another 0.015" to its jump instead, putting the bullet a total of 0.050" off the lands. He had 20 rounds loaded before he discovered the error. He considered pulling and reseating the bullets, but decided to shoot them in practice. To his amazement, the "too much jump" bullets gave him two 1/4" groups and two true bugholes "in the ones".
So, regardless of what is mostly the case, you have to try more and further bullet jump than you might suppose to be truly sure you are where you need to be. Many shooters report that once they establish the best jump for a barrel, the same gun tends to like the same jump with other bullets, though you want to confirm that when you've found a good one in a particular gun. Many also report finding two sweet spots if they go back far enough, though one will be better than the other. So there is more experimenting you could do.
You may want to read this other example from Berger.
The late Dan Hacket told of a 40X chambered in 220 Swift he had for benchrest shooting that only grouped 5 shots into about 1/2 moa no matter what bullet and load he used. He always seated 0.020" off the lands because everyone said it tended to be best and he'd had good luck with it in the past. Then one day in changing to a bullet that was 0.015 shorter than the one he had been loading, he turned his seating die micrometer the wrong way, so instead of letting it come forward 0.015 he wound up adding another 0.015" to its jump instead, putting the bullet a total of 0.050" off the lands. He had 20 rounds loaded before he discovered the error. He considered pulling and reseating the bullets, but decided to shoot them in practice. To his amazement, the "too much jump" bullets gave him two 1/4" groups and two true bugholes "in the ones".
So, regardless of what is mostly the case, you have to try more and further bullet jump than you might suppose to be truly sure you are where you need to be. Many shooters report that once they establish the best jump for a barrel, the same gun tends to like the same jump with other bullets, though you want to confirm that when you've found a good one in a particular gun. Many also report finding two sweet spots if they go back far enough, though one will be better than the other. So there is more experimenting you could do.
You may want to read this other example from Berger.
10-shot test groups are twice as good as 3-shot groups. You'll do well with them.
reynolds357
New member
You dont pay the published max too much attention for the 7x57 if you have a modern action. You can safely push it up to euro pressure spec.
The European data is here. Their value Ptmax is the equivalent of SAAMI's Maximum Average Pressure (MAP). They give it in bar instead of psi. Multiply bar by 14.5038 to get psi.
Ah, seating depth. You need to ask yourself what kind of reloader you are.
There are really two approaches to reloading, and you need to decide what your goal is:
Do you want to wring the last bit of accuracy out of your rifle?
Do you want to make ammunition that has acceptable accuracy for your application.
If the former, keep doing what you are doing.
I fall firmly in the latter camp. I started out chasing the last tenth, but after I figured out how many rounds I fired and range trips I made trying to make already good groups smaller, I stopped.
For some people, reloading is as much or more of the hobby than actual shooting, and there is nothing better than tinkering with different powders, and charge weights, and seating depths to try and eek out the best possible performance from your load and rifle. I am not that person.
What I do is set it so there is about .020" jump to the lands, assuming I can get that long and still fit in the magazine.
I then tune the load to the rifle with the powder charge. I have never had a problem finding a load that has acceptable accuracy for the application.
Is it the best possible seating depth? Doubtful, but it has always worked for me, but it will almost always be better than whatever the "OAL" number published on the loading manual says.
Yes, I admit I am leaving some potential accuracy improvements on the table. For me, it is not worth the extra effort and time, plus wear on the barrel to find that last couple tenths.
If you are getting 2-3" groups at 200 yards, that is 1 to 1.5 MOA, which is decent for a factory rifle.
There is a big difference between SAMMI and CIP pressures for the 8mm Mauser/8x57 IS , but that is beyond the scope of this conversation (but not this one, if anyone is interested).
There are really two approaches to reloading, and you need to decide what your goal is:
Do you want to wring the last bit of accuracy out of your rifle?
Do you want to make ammunition that has acceptable accuracy for your application.
If the former, keep doing what you are doing.
I fall firmly in the latter camp. I started out chasing the last tenth, but after I figured out how many rounds I fired and range trips I made trying to make already good groups smaller, I stopped.
For some people, reloading is as much or more of the hobby than actual shooting, and there is nothing better than tinkering with different powders, and charge weights, and seating depths to try and eek out the best possible performance from your load and rifle. I am not that person.
What I do is set it so there is about .020" jump to the lands, assuming I can get that long and still fit in the magazine.
I then tune the load to the rifle with the powder charge. I have never had a problem finding a load that has acceptable accuracy for the application.
Is it the best possible seating depth? Doubtful, but it has always worked for me, but it will almost always be better than whatever the "OAL" number published on the loading manual says.
Yes, I admit I am leaving some potential accuracy improvements on the table. For me, it is not worth the extra effort and time, plus wear on the barrel to find that last couple tenths.
If you are getting 2-3" groups at 200 yards, that is 1 to 1.5 MOA, which is decent for a factory rifle.
On Edit:----never mind, see below----Unclenick said:
There is a big difference between SAMMI and CIP pressures for the 8mm Mauser/8x57 IS , but that is beyond the scope of this conversation (but not this one, if anyone is interested).
Last edited:
reynolds357
New member
Samu and CIP pressures are not the same. CIP is 56565 psu SAAMI is 51000 psi.
There is no reason not to take it to 61,000 psi like most modern actions handle with ease.
There is no reason not to take it to 61,000 psi like most modern actions handle with ease.
The CIP used to require all guns to go through proof testing every time they were sold. They have stopped a lot of that as being redundant, but it did make it easier for them to be certain guns could all withstand a higher pressure than U.S. guns can be certain to do. SAAMI has no authority to impose that kind of testing, so they've been a lot more cautious about what weaker arms might be out there.
Even if they didn't have that difference in concern about the strength of some guns, they would still be measuring with the conformal piezo transducer instead of the channel piezo transducer used in Europe, so some differences would probably remain. An extreme example is the 357 Magnum. It is rated by SAAMI for 45,000 CUP and 35,000 psi. That lower psi number, just the opposite of what you see in most rifle cartridges for which the psi is usually higher than the CUP, is a measuring system artifact. Former SAAMI Technical Director Ken Green told me that for the .357 limit, they took the same lot of reference ammunition and fired it in both the copper crusher and conformal transducer, and after they got the correction factors, that lower peak number is just what the conformal transducer system produced. The CIP, meanwhile, has its channel transducer giving them 43,511 psi (actually, 3000 bar). That's a 24% higher psi measurement just due to the measuring system difference.
I don't know that the 8×57 IS is subject to that large a disagreement, but it seems likely to acount for some portion of it.
Even if they didn't have that difference in concern about the strength of some guns, they would still be measuring with the conformal piezo transducer instead of the channel piezo transducer used in Europe, so some differences would probably remain. An extreme example is the 357 Magnum. It is rated by SAAMI for 45,000 CUP and 35,000 psi. That lower psi number, just the opposite of what you see in most rifle cartridges for which the psi is usually higher than the CUP, is a measuring system artifact. Former SAAMI Technical Director Ken Green told me that for the .357 limit, they took the same lot of reference ammunition and fired it in both the copper crusher and conformal transducer, and after they got the correction factors, that lower peak number is just what the conformal transducer system produced. The CIP, meanwhile, has its channel transducer giving them 43,511 psi (actually, 3000 bar). That's a 24% higher psi measurement just due to the measuring system difference.
I don't know that the 8×57 IS is subject to that large a disagreement, but it seems likely to acount for some portion of it.