Long barrel cast bullet load warnings

[bhp9]

Having developed some super accurate loads for the 8x57 Mauser but used in the standard 23 ½ inch barrel, I was beside myself when the same load did not work in a long barreled (29 inch) Persian (Czech) Mauser. Checking out the velocity on my chronograph I discovered the long barrel was producing velocities in excess of 2,000 fps whereas the shorter barreled Mausers I have produced about 1,900 fps. I there for cut back my load from 27 grains of 4198 to 25.5 grains and all was well once again and I could use the 25.5 grain load in either long or shorter barrel rifles.

Load was 160 Grain Lyman Lovern with 50/50 alox lube, 1 grain polyester pillow stuffing, Hornady gas check and 25.5 grains of imr 4198 powder. Bullets sized to .325. Used pure Linotype metal.

[NuJudge]

How did 27 grains of 4198 shoot through the long barrel? If it shot well, had no pressure signs, and did not Lead, shoot it in the long barrel. I've run .30-'06 cast bullets over 2200 fps with no problems.

CDD

[joeb33050]

Having developed some super accurate loads for the 8x57 Mauser but used in the standard 23 ½ inch barrel, I was beside myself when the same load did not work in a long barreled (29 inch) Persian (Czech) Mauser. Checking out the velocity on my chronograph I discovered the long barrel was producing velocities in excess of 2,000 fps whereas the shorter barreled Mausers I have produced about 1,900 fps. I there for cut back my load from 27 grains of 4198 to 25.5 grains and all was well once again and I could use the 25.5 grain load in either long or shorter barrel rifles.

Load was 160 Grain Lyman Lovern with 50/50 alox lube, 1 grain polyester pillow stuffing, Hornady gas check and 25.5 grains of imr 4198 powder. Bullets sized to .325. Used pure Linotype metal.

This is perhaps an instance of where the RPMs got too high and accuracy was diminished. Would you measure and tell us the twist of each rifle? And any more info on MV, chronograph records with the loads, and group size would be welcome.
Thanks;
joe b.

[rhead]

Did you try goining up a little more if there were no pressure signs? It may have been barrel harmonics due to the different lengths of the barrel.

[Larry Gibson]

T'was the increase in RPM. I've had the same problem with that bullet (and any other for that matter) when shooting loads that develope 1800-1900 fps in the 23 1/2" 8x57 Mausers. I most often use 4895 and when shot in the longer 29" barrels the RPM is over the threchold with their 9 1/2" twists.

Larry Gibson

[45 2.1]

T'was the increase in RPM. I've had the same problem with that bullet (and any other for that matter) when shooting loads that develope 1800-1900 fps in the 23 1/2" 8x57 Mausers. I most often use 4895 and when shot in the longer 29" barrels the RPM is over the threchold with their 9 1/2" twists.

Larry Gibson

Makes you wonder just how well jacketed stuff shoots at the supposed RPM limit, doesn't it. It's a material prolem........

[Larry Gibson]

Makes you wonder just how well jacketed stuff shoots at the supposed RPM limit, doesn't it. It's a material prolem........

Definately a material problem with cast bullets for several reasons. The two primary reasons are; it is much more difficlt to cast a perfectly balanced bullet than it is to swage a jacketed bullet. Cast bullets are also subject to much more deformation during acceleration than jacketed bullets which caues defects which unbalance the bullet. The greater the imbalance the greater the adverse effect RPM has on accuracy.

Jacketed bullets are adversly effected by RPM also. Any imbalance which causes deviation between the center of gravity and the center of form will cause the center of spin to be off also. With quality bullets these imbalances are small so the effects are not generally recognised. Consistancy of the load and barrel harmonics are what most shooters pay attention to. Given a consistant load (internal ballistics) it is the RPM of the bullet during flight (external ballistics) that mostly effects the intrinsic accuracy. Bench resters and long range shooters (Palma) understand this and use the minimum twist necessary to stabilize the bullet. This also produces the least RPM decreasing the adverse effect on accuracy.

RPM is definately a more pronounced problem with cast bullets. A material problem at that.

Larry Gibson

[runfiverun]

a thought
it seems to me that with a j-bullit you should be able to predict the groupability[new word]
of your loads by basing it on rpm's.
by using acceleration variables / internal ballistics/
and powder to bore ratios
little help here

[Larry Gibson]

a thought
it seems to me that with a j-bullit you should be able to predict the groupability[new word]
of your loads by basing it on rpm's.
by using acceleration variables / internal ballistics/
and powder to bore ratios
little help here


I can give you an example;

Testing several lots of M80 (U.S.) in a M788 with 10" twist, a M70 with 12" twist and a M98 with 14" twist show results of; 3-3.5 moa in the M788, 2-3 moa in the M70 and 1-2 moa in the M98. The M788 is capable of right at moa with good loads and the other two are sub moa capable. The M70 and M98 have longer barrels (26 and 27") and produce correspondingly higher velocity than the 22" M788. The M70 and M98 thus also produce a higher RPM relative to if they had 22" barrels as the M788. Thus with M80 bullets that are not exactly of commercial hunting bullet or of match bullets. The use of those bullets in the various twists gives an excellent example of how RPM effects jacketed bullets also.

Larry Gibson

[Blammer]

jacketed bullets vs cast bullets with respect to twist and RPM are like comparing apples to oranges.

[45 2.1]

jacketed bullets vs cast bullets with respect to twist and RPM are like comparing apples to oranges.

Talk to a really good materials engineer sometime with this observation. You all could benefit greatly from it.