Does adjusting oal change MV ?

[PlinkIt]

Does adjusting the overall length have much effective change on muzzle velocity?.. I understand it will show variations in pressure when extending out towards the lands.. But is the pressure differences seen in the exercise enough to see at the chrono?..

 

[Killshot44]

Absolutely. Pressures and velocities are affected when the bullet is seated farther into or out of the case by the change in the internal volume of the case - even when the ogive is nowhere near engaging the lands.

 

[BullyDog]

Yes, your pressures can vary greatly, kind of like when you run moly coated rounds but in a different aspect.

Does adjusting the overall length have much effective change on muzzle velocity?.. I understand it will show variations in pressure when extending out towards the lands.. But is the pressure differences seen in the exercise enough to see at the chrono?..

 

[Victor N TN]

I agree with both the posts above.

 

[gstaylorg]

I would answer your question by saying changing your OAL (seating depth) MAY change your MV. It will largely depend on how much OAL change you're talking about and whether you're seating into the lands, or really far off the lands such that powder compression comes into play. For example, with a bullet like the Berger 185 Juggernaut, which is fairly insensitive to seating depth, I started them at .015" off during load development. After finding the OCW, I did a seating depth test, changing the seating depth by .003" for each set (.009", .012", .015", .018, and .021" off the lands). There was a lot of info available to suggest that this range was enough to find a sweet spot for the 185 bullet. What I can tell you is that over this range, there was no significant effect on MV.

However, if you're seating into the lands, or very far off the lands, it's a whole different story as others have mentioned above. Take a look at the following link regarding an approach for seating depth testing with VLDs from Berger:

Berger Tips for Loading VLD Bullets « Daily Bulletin

Note in the bottom half of the article that seating the bullet extremely far into the case actually raised the pressure more than jamming it. Either way, many tangent ogive bullets are relatively easy to tune for seating depth and if you're only moving the bullet within a very small window such as .010" off to .030" off, you probably won't see large changes in MV for a given charge weight. However, if you jam or jump by much larger increments, pressure can become a significant safety issue. For that reason, ALWAYS START LOW and work up gradually. It's simply not worth it to do otherwise.

 

[PlinkIt]

Thanks guys