Pressure problems question.

[Lofty]

So I'm working up a load for a new rifle chambered in 243.

My previous loadings had me pushing 115s at around 3050/3075 with no pressure signs at all.

I started with the same load but with 38 grains of H4350 instead of the 42.3 grains I had used in my other rifle.

By the time I got to 40 grains I was getting a sticky bolt and minor cratering of the primer. So I stopped, problem was, I was only getting around 2850 FPS.

I was seated .30 thou off the lands, I can't imagine why I was getting pressure issues so quick but with poor velocity.

I tried another load, 105 hybrids. I got up to 42.5 grains of 4350 before I started to see mild primer flattening but no sticky bolt. I was only getting 3050 with 105s. Seems a tad slow.



Any suggestions? I started another load up in H4381 and I'm gonna try that tommorow.

 

[cmh2007]

Re: Pressure problems question.

different barrel, different chamber, different gun. each one responds different...was it the same chrono?

 

[Lofty]

Re: Pressure problems question.

Yeah, same chrono.

I'm just wondering how I can only be getting 2800 FPS with pressure signs VS almost 3100 FPS with no pressure signs?

Same powder and bullet same distance from the lands.

Would a different powder be the answer?

 

[oldfatguy]

Re: Pressure problems question.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lofty</div><div class="ubbcode-body">Yeah, same chrono.

I'm just wondering how I can only be getting 2800 FPS with pressure signs VS almost 3100 FPS with no pressure signs?

Same powder and bullet same distance from the lands.

<span style="color: #FF0000">Would a different powder be the answer?</span> </div></div>

Bingo!


OFG

 

[cmh2007]

Re: Pressure problems question.

give you an idea, my old barrel on my .308 would drive a 155 scenar to 3000fps out of a 26 inch tube, using almost 51 grains of powder...it was on the ragged edge of starting to show pressure, it wouldn't even get close to max book load with varget before showing major pressure signs (and it would only drive the 155's at 2745). with the new barrel, I only need 48.7 grains of 2000mr to make a 155 do 3050 and have room to get just a little more out of it. it likes it just like that. the new barrel is just that much faster

 

[Lofty]

Re: Pressure problems question.

Well I went back out again today after starting over and loading up different rounds with 4350, RL25 and 4831.

With 4831 I got to 3056 FPS with 46.5 grains but was starting to get a stiff bolt lift and didn't like what I was seeing with the primers.

RL25 was zinging along but I only got up to 2937 with 47 grains. Bolt lift was easy and had no primer flow but I hadn't loaded any more ammo higher as I didn't think it would even make it that high....seems like a lot of powder.

I went back to 4350 and this time had no issues all the way to 42.3 grains at 3100 FPS and the gun was loving it. You could feel the round crack and it was drilling laser beam holes. Shot more than one sub 1/4 MOA group.

The only thing different was that I broke open a brand new bottle of 4350. The other one was only about 2 months old from the same store and I stored it indoors in air conditioning with the bottle sealed tight.

Can there be that big a variance between bottles?


It doesn't seem logical to me.....I'm thinking it was something I was doing wrong on the first batch.

 

[cmh2007]

Re: Pressure problems question.

Look at lot numbers

 

[oldfatguy]

Re: Pressure problems question.

Just re-read your thread and didn't see any mention of the brass you are using. Is it the same?

Also, the three powders you have tried are numbers: 114 (H4350), 125 (H4831), and 133 (RL25) on the burn rate chart. Of course the different burn rates will cause pressure and velocity variations, some good, some not so good. Your rifle seems to like 42.3 grns of H4350 the best for that particular bullet.

Powders can vary from lot to lot for the same manufacturer and type. Look at the lot numbers on the bottles. Are they different?

OFG

 

[Lofty]

Re: Pressure problems question.

So I got two variables then.

Just checked lot numbers and they are different. Also, the brass I used today was brand new Winchester brass. The brass yesterday was once fired Winchester which was full length resized.

I'm gonna full length resize the 20 I shot today that worked so well and recharge them with powder from the new bottle and try again.