Post by Bullshop on Jun 1, 2019 7:55:31 GMT -7
Question
hello , i picked up a marlin 45/70 last year. i had been advised not to go over 405 projectiles. so was i missinformed?? i was told anything over 405 will build to much chamber pressure. your advise is needed. thank you..
Answer
The person that advised you obviously has no understanding of the factors involved with loading ammunition and or how chamber pressures are controlled or regulated to stay within safe ranges with the components used. The single factor that determines what weight projectiles or more correctly what length projectiles will shoot well in any launch platform is the rate of twist of the rifling in the barrel. There is no safety issue but the issue is of bullet stability . The rule of thumb is that longer bullets (heavier) require more rotational velocity to remain stable in flight. The older micro groove Marlins had a rifling twist rate of one turn in 20” as do I believe the newer Ballard rifled barrels.. On average a 1/20” twist rate will stabilize bullets of the correct nose shape for Marlins (flat nose) to slightly over 500gn. I have a pre-micro groove Marlin with 1/20” twist that shoots extremely well with the RCBS 525gn FN-GC bullets and even shoots well with our 550gn hollow point gas checked bullet design. Currently in long range competition 45-70 rifles are being rifled with 1/18” and even as fast as 1/16” the reason being so they will stabilize even longer heavier bullets to capitalize on the higher ballistic coefficients of the longer heavier bullets and their enhanced long range performance. If load development is progressively worked up and ends within safe pressures bullet weight/length is never an issue . The issue will be accuracy. Bullet length/weight longer than can be stabilized with your rifling twist rate simply will not shoot good and will show tipping or even tumbling passing through paper targets.