Fireforming Pressures

[azsugarbear]

The purpose behind using cornmeal to fireform cases is: barrel life. In my case, I was fireforming 277 Allen Magnum cases from 338 Lapua brass. Expected barrel life on the 277 AM is anywhere from 600 to 1000 rounds. Remember, you are sending 90+ grains of burning powder into a .277 funnel at very high pressures. When you are spending $750 on the barrel ($400 for a custom fluted barrel and another $350 on smithing for threading, chambering, crowning and brake indexing), you don't want to spend even 50 rounds fireforming cases with bullets and semi-full to full loads. 10-20 grains of a fast-burning pistol or shotgun powder under cornmeal gets the job done with minimum barrel wear. It's all about barrel life - not the bang in the air.

 

[Lefty7mmstw]

When you have to scrub the hell out of the barrel to get the burned mess out it negates a lot of the savings in bore life you think you'll get. I've done both ways in a previous 7 stw. I'll shoot mild loads and watch barrel heating before I'll ever touch cornmeal again. I'm "on the wagon" on cornmeal and pistol powder. Half of your barrel life on these rounds is letting the barrel heat anyway.
Take it out in zub- freezing temps if bore life bothers you. She'll cool a lot better. I've got some below zero coming up here; it's like getting a free lunch on bore life as you really can't heat them up.

 

[azsugarbear]

As I understand it, barrel life or throat erosion is not just about heat, but rather heat combined with pressure. Hence the aligator skin appearance in the throat area only and not the entire barrel. The cornmeal loads do not develop anywhere close to the kind of pressure that a live round does.

I'm not aware of any studies confirming wear difference between the cornmeal and reduced loads on the barrel when case forming. I have not found the cornmeal method to be particularly messy, but each of us have our own experiences. The gunsmith who built this rifle was Kirby Allen. Never met the man, but I like his appraoch and common sense in all matters involving shooting. I suspect he has forgotten more about shooting a rifle than I will ever know. He recommended the cornmeal method to me and has even posted a thread on it here several years ago. I'm just trying to offer J300UM another alternative.

 

[big wally]

The purpose behind using cornmeal to fireform cases is: barrel life. In my case, I was fireforming 277 Allen Magnum cases from 338 Lapua brass. Expected barrel life on the 277 AM is anywhere from 600 to 1000 rounds. Remember, you are sending 90+ grains of burning powder into a .277 funnel at very high pressures. When you are spending $750 on the barrel ($400 for a custom fluted barrel and another $350 on smithing for threading, chambering, crowning and brake indexing), you don't want to spend even 50 rounds fireforming cases with bullets and semi-full to full loads. 10-20 grains of a fast-burning pistol or shotgun powder under cornmeal gets the job done with minimum barrel wear. It's all about barrel life - not the bang in the air.

Ok you got me on that i expect my rifle barrels to last thousands of rounds and even when the groups open up they will still be game getters.
I cant see myself ever buying a gun that will need a new barrel at 1,000 rounds so i stuck my oar in and never been in a boat like that.
Sorry.
Wally

 

[Lefty7mmstw]

As I understand it, barrel life or throat erosion is not just about heat, but rather heat combined with pressure. Hence the aligator skin appearance in the throat area only and not the entire barrel. The cornmeal loads do not develop anywhere close to the kind of pressure that a live round does.

I'm not aware of any studies confirming wear difference between the cornmeal and reduced loads on the barrel when case forming. I have not found the cornmeal method to be particularly messy, but each of us have our own experiences. The gunsmith who built this rifle was Kirby Allen. Never met the man, but I like his appraoch and common sense in all matters involving shooting. I suspect he has forgotten more about shooting a rifle than I will ever know. He recommended the cornmeal method to me and has even posted a thread on it here several years ago. I'm just trying to offer J300UM another alternative.

Barrel steel is much more resistant to the rigors of firing if it is at colder temperatures. I won't even take my 300 rum or 7 stw out in 100 degree temps; I save those two for cooler days and shoot one of my 270's or one of my bigger bore rifles if the temp. is that bad. You will get a certain amount of wear no matter what because of the heat and pressure when fired, but damage to your rifle from shooting it will be less and your ultimate round count when retiring the barrel will be a lot higher if you never let her heat and shoot when cold out. I also try to never shoot absolute max. loads as a few thousand psi less will also help with bore life quite a bit.

 

[azsugarbear]

Big Wally,

There's no right or wrong here, just different needs. When my big 338 Lapua Imp. gets built, I will probably use your way, as I expect barrel life to be much longer. I hope to shoot with you someday, if you ever hop the pond. BTW, Wales is close to my heart, as my family originally came from there.

Left7mmstw,

I hear you on temps. Unfortunately, I live in AZ. For half of the year, temps are over 100. From a shooting perspective, I envy your location. The next four months should be good for us down here in Phx.

 

[big wally]

Barrel steel is much more resistant to the rigors of firing if it is at colder temperatures. I won't even take my 300 rum or 7 stw out in 100 degree temps; I save those two for cooler days and shoot one of my 270's or one of my bigger bore rifles if the temp. is that bad. You will get a certain amount of wear no matter what because of the heat and pressure when fired, but damage to your rifle from shooting it will be less and your ultimate round count when retiring the barrel will be a lot higher if you never let her heat and shoot when cold out. I also try to never shoot absolute max. loads as a few thousand psi less will also help with bore life quite a bit.

What the hell is 100degrees i dont think i have ever been in anything over 80 degrees and if i am all the family will be standing around holding flowers and hopefully crying and asking have you found his money yet.
Wally

 

[big wally]

Big Wally,

There's no right or wrong here, just different needs. When my big 338 Lapua Imp. gets built, I will probably use your way, as I expect barrel life to be much longer. I hope to shoot with you someday, if you ever hop the pond. BTW, Wales is close to my heart, as my family originally came from there.

Left7mmstw,

I hear you on temps. Unfortunately, I live in AZ. For half of the year, temps are over 100. From a shooting perspective, I envy your location. The next four months should be good for us down here in Phx.

Yes we little Welsh buggers get everywhere dont we my nephew has come to live over the pond after marring an American girl they live in Bradford Vermont.
and Mark dont shoot but his wife Shelby,s family are big hunters
Wally

 

[Lefty7mmstw]

Big Wally,

There's no right or wrong here, just different needs. When my big 338 Lapua Imp. gets built, I will probably use your way, as I expect barrel life to be much longer. I hope to shoot with you someday, if you ever hop the pond. BTW, Wales is close to my heart, as my family originally came from there.

Left7mmstw,

I hear you on temps. Unfortunately, I live in AZ. For half of the year, temps are over 100. From a shooting perspective, I envy your location. The next four months should be good for us down here in Phx.

When we get as cold as tonight willl be I'd rather be where you are. It'll hit -20 here tonight if it goes anywhere. It was -6 when I shut the truck down this afternoon and rather windy. I won't even try to drive my car tomorrow; my Volt hates it below zero so I'll leave it plugged in and drive my Durango. Dodge trucks will usually start to -40 without using a block heater. I've seen -45 with my last dodge.

As far as fireforming using loaded ammo; shooting a slower cadence, ie. a round every few minutes while you are working with something else will help a lot. Using just enough pressure for a good fill will also help; you don't need b#11s to the wall stuff for fireforming.