Changing primers during load development?

[Spothogg32]

Hey guys I am in the final stages of my load development for my 7mm Remington mag custom rifle. My rifle is built on a Remington 700 action that has been rebarreled with a Broughton 5.5 5C 1 in 9" twist 26" barrel. My goal was to push a Berger 180gr VLD at 3000fps. I reached that goal today with my final load. The load consisted of a 180gr Berger VLD, 72gr of H1000 and a CCI 250 primer loaded at a COAL of 3.540" .o15" off the lands. My average velocity for a 5 shot string was 3008fps with an extreme spread of 29.8fps the group measured less than .75" center to center. I would like to get the extreme spread down a little more so my question is If I were to go to a CCI 200 or Fed 210 primer and keep my load at 72gr of H1000 do you think my pressure would increase, decrease, or stay the same. I was hoping not to reduce my load and have to work up again but if you guys have experienced pressure problems by going to a cooler primer then I guess I will have to start over.

 

[johnnyk]

SpotHogg32,
All the reloading instructions say anytime you change components, drop the powder chage and work up. This really applies when you near max load. Here are a couple of links, hope they help in your quest/decision.

Primer cross reference chart

Primer Testing Reference

JohnnyK.

 

[J E Custom]

Sometimes going from a magnum primer to a non magnum primer will improve SDs.

Magnum primers will normally increase velocity but be more erratic, and a non magnum
primer can make for a more consistant powder burn.

Its worth a try.

J E CUSTOM

 

[trebark]

Especially when you change primers, you need to back your powder charge down and work your way back up. I had a load for my 260 that I developed with the F210(not match) and wanted to see if the ES would reduce if I changed to the F210M. Turns out the F210M showed pressure signs with the same powder charge.

 

[Bart B]

The load consisted of a 180gr Berger VLD, 72gr of H1000 and a CCI 250 primer loaded at a COAL of 3.540" .o15" off the lands. My average velocity for a 5 shot string was 3008fps . . . .

Hodgdon lists their max load for a 175 grain bullet as 64.5 grains of H1000 producing about 2700 fps in a 26 inch barrel peaking at about 50,400 CUP. If you are loading 72 grains behind a 180-gr. bullet, I believe 3000 fps is possible.

I also believe your pressure is dangerously too high.

 

[Edd]

Hodgdon lists their max load for a 175 grain bullet as 64.5 grains of H1000 producing about 2700 fps in a 26 inch barrel peaking at about 50,400 CUP. If you are loading 72 grains behind a 180-gr. bullet, I believe 3000 fps is possible.

I also believe your pressure is dangerously too high.

They also show the maximum load for a 7mm Weatherby magnum to be 74.7 grains of H1000.

 

[Spothogg32]

Hodgdon lists their max load for a 175 grain bullet as 64.5 grains of H1000 producing about 2700 fps in a 26 inch barrel peaking at about 50,400 CUP. If you are loading 72 grains behind a 180-gr. bullet, I believe 3000 fps is possible.

I also believe your pressure is dangerously too high.

Man I tell you one thing this Broughton barrel is an incredibly low pressure barrel! When I started my load development with the Berger 168gr VLD I used their load information that they provided me with. the max load was supposed to be 70.5gr of Retumbo I started at 68gr and worked up to my top load in .5gr increments. When I shot my first 5 shot string with the 68gr starting load I had dangerously low pressure signs. all 5 cases had powder residue all the way to the belt. I had never experienced anything like that before. It took a few increases in powder before the residue started moving toward the sholder of the case. When I finished working up the loads with that bullet and Retumbo powder I was at 74gr of Retumbo with a little residue on the neck of the case which I am used to seeing and absolutely no sign of pressure. No sticky bolt lift, no plunger marks, and primers were not bad either. The final average velocity was 3056fps but the ES was in the 60fps range which is not good. I have since switched to H1000 and the ES is better it is in the 30fps range but I am still not happy with that so that is my reason for playing with the cooler primers I hear that sometimes that helps improve the ES. I have decided it is a good idea to reduce my load and start over with the GM210 primers and see what the results are Thanks for all of your imput everybody. I will let you know how it goes!

 

[Spothogg32]

SpotHogg32,
All the reloading instructions say anytime you change components, drop the powder chage and work up. This really applies when you near max load. Here are a couple of links, hope they help in your quest/decision.

Primer cross reference chart

Primer Testing Reference

JohnnyK.

Johnnyk,

Thanks for the links this was great information I am going to give the GM210 primer a try and reduce my load and work up again!

 

[Bart B]

Man I tell you one thing this Broughton barrel is an incredibly low pressure barrel!

Hope your 7mm barrel's not like a 30 caliber one a friend had some years ago. He had it fitted and chambered for .30-.338 then started working up loads. At several grains over published max, he decided to have the bore/groove dimensions checked. They were .303" and .311" instead of the normal .300" and .308".

He called Douglas Barrels and asked why his 30 caliber barrel had way oversize bore and groove diameters. Douglas said they probably mismarked a rifled blank made for 7.65 Argentine Mauser or .303 British as a 30 caliber one.

If your barrel belonged to me, I'd check its bore and groove diameters.

 

[Spothogg32]

Hope your 7mm barrel's not like a 30 caliber one a friend had some years ago. He had it fitted and chambered for .30-.338 then started working up loads. At several grains over published max, he decided to have the bore/groove dimensions checked. They were .303" and .311" instead of the normal .300" and .308".

He called Douglas Barrels and asked why his 30 caliber barrel had way oversize bore and groove diameters. Douglas said they probably mismarked a rifled blank made for 7.65 Argentine Mauser or .303 British as a 30 caliber one.

If your barrel belonged to me, I'd check its bore and groove diameters.

I do not know if you are familiar with the 5C canted lands barrel that Broughton produces but they advertise on their web site that it reduces breech pressure and can increase velocity with very low fouling biuld up for easy cleanability. All of these things I have experienced with this barrel and I have shot groups at 100 at 1/3 to 1/4 moa with the gun. I also have a buddy that has a 300 UM and 338 UM with these barrels with similar results.

 

[Reloader222]

Changing primers is like changing the octane of the fuel onyour 1970 model Ford. You need to fine-tune the carburator for peak performance. Each kind of primer has it's ideal load combination for peak performance.

 

[Spothogg32]

Well guys, I made it to the range today with some new loads that I worked up in .5gr increments using the fed gm210m primer and was very pleased with the results. I shot 5 different 5 shot strings with the 5 different loads and my ES improved a bunch I finally made it into the 12 to 15 fps range for 5 shots! I finished the day with my final load with a 180gr Berger VLD with 72gr of H1000 with a COAL of 3.540" and an avg. 5 shot velocity of 2972fps. My velocity with the CCI 250 magnum primer was only 36fps faster with the same charge. My groups were also holding right at 1/2 MOA or less for 5 shots. An other interesting thing I noticed is the primers on all 25 cartridges had not really started to flatten they just had the primer dent in them and that was basically it with no other signs of pressure! the CCI 250 primers were slightly flattened at the starting load of 70gr and stayed basically the same with the finishing load of 72gr. My next trip out I plan on loading up to 73gr to see if I can get back to the 3000+ fps that I was at before and see if I can maintain the 1/2 MOA accuracy. After that I plan on playing with my seating depth with the Bergers to see if I can get it closer to 1/4 MOA like I did with the 168gr Berger. For some reason the 168gr liked a bunch of jump start .o63" off the lands. Thanks for all of your input and good luck on all of your ventures!

 

[Boss Hoss]

Edited

 

[Bart B]

I do not know if you are familiar with the 5C canted lands barrel that Broughton produces but they advertise on their web site that it reduces breech pressure and can increase velocity with very low fouling biuld up for easy cleanability.

That's a good thing. But Broughton should make accurate pressure measurements with strain gages then list load data; all in accordance with SAAMI standards.

SAAMI test barrel's chamber and bore specs are different that Broughton's but if they provide these specs along with load data from standard pressure barrels, then folks will know for sure what loading data is accurate. Otherwise, 'cause the rest of us mortals are poor judges of pressure when it comes to reading case and primer deformations. And SAAMI pressure test barrel specs are based on conventional rifling with land and groove dimensions tightly specified dimensionally so Broughton's pressure test barrels should be also.