What do I do now?

[gemini1]

Thanks John. Yeah I have the Frankford kinetic bullet puller.
I'm actually thinking of pulling the bullets out of my other test batch with 22.5 grs load, and try the other batch loaded at 23.0 and 23.5

The only other issue that bugs me is bullet length. My generic bullets are shorter than the M855 and the Freedom Arms 62 grs penetrator I had just pulled for comparison.



The green tip M855 has a load of 24.4 grs, the bullet is 0.903.5" long while the Freedom Arms reload has 23.5 grs and the bullet is 0.907" My generic bullet is only 0.824" long

Would the shorter bullet create a higher pressure compared to the longer ones?
Although I will be starting at the minimum load, and find the sweet spot for the bullets I have, does it mean that if I buy say the bulk 62 grains pulled bullets or a different brand of same weight, but longer than the ones I have, I need to start again at the minimum and work up my loads?

[Wrangler John]

Thanks John. Yeah I have the Frankford kinetic bullet puller.
I'm actually thinking of pulling the bullets out of my other test batch with 22.5 grs load, and try the other batch loaded at 23.0 and 23.5

The only other issue that bugs me is bullet length. My generic bullets are shorter than the M855 and the Freedom Arms 62 grs penetrator I had just pulled for comparison.



The green tip M855 has a load of 24.4 grs, the bullet is 0.903.5" long while the Freedom Arms reload has 23.5 grs and the bullet is 0.907" My generic bullet is only 0.824" long

Would the shorter bullet create a higher pressure compared to the longer ones?
Although I will be starting at the minimum load, and find the sweet spot for the bullets I have, does it mean that if I buy say the bulk 62 grains pulled bullets or a different brand of same weight, but longer than the ones I have, I need to start again at the minimum and work up my loads?

Bullets of the same weight that differ in length usually do not effect pressure significantly. The difference between your longest and shortest bullet is .083", the determining factor is why are the bullets different and where is the difference in length located?

First thing you will notice is that the bullet on the left, the shortest, has the canelure located lower on the shank and a shorter boat tail than the center and right bullets.

The center and right bullets have the cannelure set higher and longer boat tails, but for all practical purposes are the same length, .907" (Freedom Arms) and 903.5" (M-855).

That deeper cannelure on the M-855 and Freedom Arms bullets will require seating deeper into the powder space to crimp, which will have the effect of raising pressure above that of the shorter generic bullet. Your shorter generic bullet being seated out increases powder capacity which lowers pressure for any given load. The other factor affecting pressures is whether or not the mil-spec load has a bullet sealer applied for water proofing, that can also cause a slight increase in pressures. Is that darkened area on the M-855 bullet's boat tail a sealer residue or a photographic artifact?

Longer bullets are generally heavier and have a longer bearing surface, the portion of the bullet that contacts the bore diameter, all of which raises peak chamber pressure. Lighter bullets conversely have a shorter bearing surface, which coupled with their lighter weight, take less pressure to get moving and engrave into the rifling, lowering peak chamber pressure.

If you were to measure the actual length of your example bullets, using a bullet comparator, it appears that all three have a similar length bearing surface. The difference in length is found in the boat tail and ogive length, which are not in contact with the bore.

There are other factors, such as jacket and core composition which also effect pressures, such as monolithic copper bullets which are solid copper with an internal expansion cavity. An example would be the Barnes Bullets product, which have circumferential grooves cut into the bearing shank to reduce pressures by reducing bearing surface and allowing jacket material displaced by the rifling a place to bleed off.

The other effect between shorter and longer bullets is found in rifling specifications. Longer bullets require a faster twist to stabilize than shorter bullets.

In most cases heavier bullets are longer, lighter bullets are shorter, especially with lead core bullets. The exception is monolithic copper and jacketed powdered metal core bullets. Lead free varmint bullets, such as the Barnes Varmint Grenade, have cores of compressed powdered copper that is a solid resembling a stick of chalk in consistency.These bullets are very long for their weight. A 50 grain .224" Varmint Grenade is .855" in length, requiring a minimum twist rate of 1:10" with 1:9" of faster being better. Bullets with penetrators will usually be longer if the penetrator material is lighter than lead.

If we take a look at stability of your longest and shortest bullets we find that at 3,000 fps your generic bullet will stabilize in a 1:10" rifling twist with a stability factor of 1.590 (anything above 1.3 being stable). Your longest bullet will stabilize in a 1:9" rifling twist with a stability factor of 1.489. So that the generic bullet will be easier to stabilize in any twist rate faster than 1:10". You can check your bullet stability factor here: http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi they also offer an extensive selection of other ballistic calculators.

If you are comparing powder charges of factory loaded ammunition versus handloaded charges, there is no way to know what powder was used in any given lot of factory ammunition. I would not trust any information regarding factory powder specifications as most of these powders are not available to handloaders in canister grade uniformity. Only use data published by powder manufacturers or in loading manuals.

When changing a load for any given bullet of the same weight it is good practice to begin at the minimum load and work back up. This will also demonstrate if the new bullet prefers a slightly lower charge. In my opinion, the shorter bullet will not raise pressures for any given load used with the longer bullets of equal weight. Whether or not it will develop more consistent accuracy depends on so many variables that actual shooting is the only way to know - more fun anyway.

[gemini1]

Wow! John, I'm still digesting your lengthy but info rich response. Thank you very much.
Yes that residue is black tar on the 855, it was still sticky when I reloaded the bullet back to its mother case.
So with the shorter bullet having the same bearing surface as the m855/Freedom, does that mean these three projectiles should have the same velocity if say I were to reload it using my own prep case primer and powder?