Success - 75 grain HPBT in 1:9 twist ;)

[Eb1]

Well keeping my word, I went and shot some reloads I put together using extruded and ball powder, 75 gr Hornady HPBT, SRM Primers, my Colt HBAR 1:9 twist.

I shot at 100 yards using open sights. The load still needs to be chrony'd. I will get that next week.

I shot the extruded powder, and they were a little all over the place. The group was a lot smaller than the A-Max bullets (longer bullet, same weight) using the extruded powder, but that is the only promise they showed. I basically gave up on the extruded powder and this weight/length bullet in my gun.

I then shot the ball powder loads. WOW! The first group was 1 1/4". I had 3 more groups to shoot. The second opened up a lot. The third group with ball powder was the ticket. Less than 1/2" and totally destroyed the X in the X-ring. I could not tell looking through the spotting scope what was going on because all the bullets were basically in the same whole.
The forth started to string. The 4th group is .5 below max. I will try the max load, but I think that the middle of the road, 3rd group is going to be my go to.

Now I need load up 20 of these loads, and take the chrony with me to the range for verification. Then will be to shoot at 200/300/600 to verify that I have a loading that can be used for HighPower.

I really need to just shoot them at 600 because the 69 SMK is shooting really good from my gun, and should be good for the 200/300 yard relays.

 

[NCsmitty]

Are you shooting 5 shot groups? 75gr bullets out of a 1in9 twist is on the ragged edge of stability, so you're going to need all the velocity you can get.
I hope it works for you, but the 69's should work all the time. I'm curious what the 75's chrono at. Are you using H335?

NCsmitty

 

[Eb1]

yep and yep.

5 shot groups for this initial test, and H335 for powder.

2.250 OAL
22.0 gr H335.


Of course I am interested in the velocity. This is why I mentioned taking the chrony next time with my lot of 20 rounds for testing.

5 shot groups were shot today.

21.0 = 1 1/4"
21.5 = 4"
22.0 = 1/2"
22.5 = 1 1/4" , but were stringing.

Max is 23.0 I think with a 75 grain VLD. According to Hodgdon's sight. Other books I have say the same with a 75 grain bullet and H335.

Yes, it is the upper limit, but with the length being .985" or so for the bullet. The equation states a 9.3" twist for this bullet with a velocity of 2700 fps.

inputs outputs
bullet length = .985 in twist 9.3 in
bullet diameter= .224 in
muzzle velocity= 2700 fps

http://kwk.us/twist.html
Regardless. 0.990 anywhere from 2700 to 2800 fps the twist is over 1:9 inches.

Don't want to really get into a debate about why/when/how. The thing I wanted to prove is that statements like this "75 grain is too heavy for a 1:9 twist." are not valid. Math dictates in this scenario.

It works in my rifle, and that is all I care about. When others have questions they need to test for themselves. Believing what you are told 100% of the time is weak. IMO

Thanks, NCSmitty. I see you on here a lot giving some pretty good advise. I am going to continue shooting these bullets until the gun decides a 75 grain HPBT cannot be shot out of it, or learns to read and starts believing what it reads on the internet.

 

[NCsmitty]

Eb1, what barrel length are you working with? If it's longer than 16" you may have room for improvement using a tiny bit slower powder to achieve higher velocity. I can feed you some data if you're flexible.

NCsmitty

 

[Eb1]

NCSmitty, I am game. Send it on over.

I am using a 20" Colt HBAR 1:9 twist. I went yesterday looking for Reloder15 or Varget, but could not locate them. I had some H335 in the closet. I decided to use it. I use H4895 for the most part, but I wasn't having as good results with it and the 75 grain HPBT as I was with the 69 grain SMK.
For some reason I just had a hunch that ball powder would be better for me and heavier bullets.

I am all up for getting a little more velocity, and possibly keeping or gaining accuracy as well.

 

[ForneyRider]

69gr SMK and 75gr Hornady BTHP are about the same length.

I think there is a 73gr Berger about the same length.

The 75gr Berger VLD and 75gr A-Max are longer.

I use R15 in these bigger bullets.

 

[Gewehr98]

That's good to know.

My 20" Colt Competition HBAR with 1-9" twist doesn't shoot bullets heavier than 69gr worth sour owl poop.

I'd be interested to see how your targets look past 100 yards, truthfully.

You may very well be on the ragged edge of stability with that rate of twist and bullet weight.

However (and this is something folks don't think of real often), it's not as much a function of bullet weight vs. rate of twist as it is a function of bullet length vs. rate of twist.

The Greenhill formula is merely a quick expedient that works most of the time.

If that 75gr bullet approximates the length of a 69gr or lighter bullet, you're probably good to go.

 

[Eb1]

Gewehr98, I think I know where you are coming from.

http://thehighroad.org/showthread.php?t=438018


I will load up 30 rounds, and go shoot them at 100 and 200 yards this weekend weather permitting and time permits. I will post the target.