seirra 140 bthp

[sifer0425]

evening
need some help on this one. did a load test on a rpr rifle with a IBI barrel 1/8 twist 26inch barrel shooting seirra boattail hollow points 140gr, .005 off the lands and using h4350 powder. cant seem to find a flat node anyway. other than maybe 40.3 to 40.6 grains of powder. any suggestions would be helpful other than maybe in the 41.2 grains had 2 rounds 41.5 and 41.8 grains couldnt load so maybe in that range but dont want to run to hot
thanks

 

[Newbie2020]

That’s because velocity flat spots don’t really exist. There’s a thread on this. In the useful range, until you get into very high pressures, velocity increases linearly w increasing powder charge.

Choose a powder weight based on your desired velocity, tune seating depth, and go shoot.

 

[918v]

evening
need some help on this one. did a load test on a rpr rifle with a IBI barrel 1/8 twist 26inch barrel shooting seirra boattail hollow points 140gr, .005 off the lands and using h4350 powder. cant seem to find a flat node anyway. other than maybe 40.3 to 40.6 grains of powder. any suggestions would be helpful other than maybe in the 41.2 grains had 2 rounds 41.5 and 41.8 grains couldnt load so maybe in that range but dont want to run to hot
thanks

I do several ladders at different COAL ranges. I have found that when you do a ladder close to the lands you get weird pressure. For example you increase the charge but the velocity goes down. That’s why I start .050” off. If I don‘t get what I want then I try .100” off and as a last resort I go close to the lands.

Bullets that have a running start engrave easier than bullets sitting right at the lands.

Also, I use 1x fired brass for this as new brass behaves differently.

 

[Baron23]

evening
need some help on this one. did a load test on a rpr rifle with a IBI barrel 1/8 twist 26inch barrel shooting seirra boattail hollow points 140gr, .005 off the lands and using h4350 powder. cant seem to find a flat node anyway. other than maybe 40.3 to 40.6 grains of powder. any suggestions would be helpful other than maybe in the 41.2 grains had 2 rounds 41.5 and 41.8 grains couldnt load so maybe in that range but dont want to run to hot
thanks

Am I reading your chart correctly? You shot one round at each load weight? I have zero expertise in reloading but I do know just a bit about statistics and one shot per charge ain't going to really show you much.

My 6.5 manbun likes to run about 2,800 fps which is right around your 41.2, no?

any idea from factory load chrono data what your rifle seems to prefer in speed?

 

[918v]

The point of a ladder test is to shoot one shot per charge weight.

 

[Baron23]

The point of a ladder test is to shoot one shot per charge weight.

But I don't see anywhere where he said he was doing a shooting ladder test.

Maybe that's what he did but he said he was looking for a node so absent any other info it seemed like he just did chrono work.

Or maybe my reading comprehension is low today...haha

Maybe he will reply and clarify.

 

[sifer0425]

just a ladder load test. did it with hornady bthp and found a node at 40.3 grains, using them. now using sierra 140 bthp and dont see and nodes or flats was told by the barrel maker that the high peak is were i need to be and just work from there

 

[Newbie2020]

Flat spots are a myth.

 

[Mike Casselton]

My 6.5 manbun likes to run about 2,800 fps which is right around your 41.2, no?

Someone say Manbun?

 

[Baron23]

Someone say Manbun?

View attachment 7651826

I really like my 6.5 man bun.....you got a problem with that? hahaha joking

Is that photo shopped or a decal? Prob not a decal but wow....if it was I think it may be a popular item. haha

 

[Mike Casselton]

Laser etched into my new Bartlein LH gain twist.

Deep South Tactical did the work.

 

[FCS]

140 SMK would benefit from 0.040” or so jump. Zero reason to be 0.005” off lands.

Distance off lands is not as useful as overall length when touching lands and/or x.xxx” off lands.

Brand of brass?