Two loads, same sights

[SauconValley Shooter]

Good Morning,

Joanna and I are going to be shooting 625s exclusively until USPSA revolver Nationals. We will shoot four inch 625s in IDPA and our USPSA 625s (5 and 6.5 inch) in USPSA, ICORE and steel matches. I would like to have two loads to shoot but I do not want to have to change the sights.

A quick look at numbers gives me 165 power factor with 230 grain bullets at around 720fps. Using 200 grain bullets with the same speed would be around 145 power factor. This would work out well as some of the local steel matches are limited to 150 power factor. In reality it will be more like the heavy load at 170 and the light load just under 150 power factor. I am assuming that point of impact will be fairly consistent if the bullet velocity is the same.

Has anyone done this?

[Dragon11]

I don't know if it would work but can you keep the same bullet weight but just lower the powder amount. I shoot the same load for my 4 inch 625 that I do with my 5 inch 625. For USPSA I shoot 230 grain Bayou bullets with 3.9 grains of Clays, which puts me around 172 power factor. I get faster velocities out of my 4 inch then I do my 5 inch. I know others here have more knowledge then I do about this topic, but if you could adjust the powder to bring you around 150 power factor from 165 power factor then you wouldn't have to change much.

Edited March 22, 2013 by Dragon11

[Carmoney]

Generally, all other things being equal, a lighter bullet will impact the target at a lower point than a heavier bullet.

My recommendation--keep the 625s dialed in for your major match load and get an 8-shot 627 for the steel matches!

[MrBorland]

I agree with Carmoney - at handgun ranges, it's bullet mass, not velocity, that affects POI. If you want to use your 625 for both, I'd pick one bullet and use 2 different powder charges.

[Matt Griffin]

Wouldn't it be load recoil more than anything else? I would think the difference in gun movement during firing would have the most impact.

[brnhp35]

My under standing is based on same powerfactor using differnt weight bullets where the lighter impacts lower because of its increased speed it leaves the barrel sooner in the recoil cycle therefore hit lower than the heavier and slower projectile. ..Kinda counter intuative but seems to be the case.

[MrBorland]

My under standing is based on same powerfactor using differnt weight bullets where the lighter impacts lower because of its increased speed it leaves the barrel sooner in the recoil cycle therefore hit lower than the heavier and slower projectile. ..Kinda counter intuative but seems to be the case.

It's time- (and therefore velocity) independent because the relevant movement of the muzzle is that which happens while the bullet's still in the barrel. IOW, a slow bullet is in the barrel longer, but the muzzle spends more time rising during this time as well. A fast bullet spends less time in the barrel, but the muzzle spends correspondingly less time rising, so net muzzle rise is the same for the same bullet, no matter the speed.

OTOH, conservation of momentum says a relatively heavy bullet (or a light gun, or a long barrel) causes the muzzle to rise more than a light bullet would while the bullet's still in the barrel, leading to a higher POI.

Clear, right?

[seanc]

Wouldn't it be load recoil more than anything else? I would think the difference in gun movement during firing would have the most impact.

With Matt on this...

For the distances you are talking about, 99% inside 20 yards, the poa/poi is going to be negligible unless you are on the fringe of some crazy slow load.

You are really only adjusting recoil and will probably find a 150pf 200g load feels pretty similar to a 175pf 230g load...my experience anyways.

[Carmoney]

Depends on what you consider "negligible." I'll bet the difference would be enough to notice at 20 yards.

[Bubber]

SVS, They were a lot of shooters who did what you are proposing, Same Load different bullet. It worked out for them as they ahot ICORE and USPSA with the same revo and same loads. The only caveat is that some powders are easier to do this with. It would take a little trial and error or you can just get lucky. You definantly need a chrony to be sure. I knew of a guy that used WW 540 for 160 and 135 grain bullets In the old Caspians with the Dual Port Compensater to change from minor to major in USPSA matches. I don't want to mention his name because I eer I mean ...HE .. may lose his status of a revo shooter later rdd

[seanc]

Depends on what you consider "negligible." I'll bet the difference would be enough to notice at 20 yards.

True for sure.

Negligible for me is less than 2" at 20 yds. On most scoring surfaces, If I am reasonably close to the center I will be OK.

Good enough for club matches.

And as I write that it doesn't really seem so good anymore, so I guess I am off base.

If your sights have repeatable clicks you can always adjust when switching loads right?

Certainly for the major matches, I would want no such variance.

[Steve RA]

Make up some loads and go try them. That is the only way you will know for sure.