I was corresponding with a gunsmith with a lot of experience with the Marlin 1895 rifles. He is a busy guy, and I don't want to bug him with questions that keep him away from his work. So I figured maybe someone here can explain something he said in reference to my rifle's ability to shoot either Buffalo Bore or Garrett heavy bullets.

"the lead in angle is 4 degree and needs to be 1.5 for less pressure and recoil"


I assume that by lead in he is referring to some aspect of the chamber. Is that correct? how does it effect recoil and pressure?

Thanks for anything that you can contribute to my education.
-cadjak

Ok..got the chamber...then a short area ahead of the chamber without any rifling (the "throat" or the "lead" or the "free bore" ..take you pick). Where the rifling actually starts is not an abrupt angle, it's tapered. In the real world, these three parts (chamber...lead...ball seat) are interdependent...changing one in isolation seldom gets results.

The angle of that taper varies from maker to maker...from a very steep/abrupt start to a long gradual tapered start. Keep in mind, we are talking about the rifling lands and not the area before rifling starts.

(ever take a look at a revolver's forcing cone...that's what i'm talking about with "ball seat"...the taper of the rifling lands)

Idea is that the long gradual taper kind of eases bullets into the rifling...was very popular in Europe when they tended to use mild steel jacket material (and is still used in some European ammo). It does slighly lower the pressure of engravment, and that lowers peak pressure slighlty.

What your gunsmith wants to do it make this angle less steep... more gently easing the bullet into the rifling and spreading out the pressure spike from engravment. What it will also do is lengthen the distance the bullet has to travel before being fully engraved.

Some examples:

The German specifications (1939) for the 8X57 usually uses a 17.2 Min. of anle taper. the typical us made 30-06 used one of 1 degree 22 minutes....why? The Gernams were using a lot of steel jacketed hunting ammo, we wre using typical jacketed ammo.


A quote for the British textbook of Small Arms (1929):

"the shorter this free travel and the steeper the angle, the greater the resistance to forward motion and the quicker and higher the gas pressure rises."

Personally, I'd not bother to change it...through load "juggling" can find a cast bulelt load that shoots well in the standard barrel....and if you can't find it after exhasutive searcing and testing, then think about changing.

Whoa!! That was great. If you don't already teach this stuff, you should. If I can understand something like this without diagrams and pictures, just from your words, you have done a spectacular job of explaining.
Thanks,
-cadjak

Ok..got the chamber...then a short area ahead of the chamber without any rifling (the "throat" or the "lead" or the "free bore" ..take you pick). Where the rifling actually starts is not an abrupt angle, it's tapered. In the real world, these three parts (chamber...lead...ball seat) are interdependent...changing one in isolation seldom gets results.

The angle of that taper varies from maker to maker...from a very steep/abrupt start to a long gradual tapered start. Keep in mind, we are talking about the rifling lands and not the area before rifling starts.

(ever take a look at a revolver's forcing cone...that's what i'm talking about with "ball seat"...the taper of the rifling lands)

Idea is that the long gradual taper kind of eases bullets into the rifling...was very popular in Europe when they tended to use mild steel jacket material (and is still used in some European ammo). It does slighly lower the pressure of engravment, and that lowers peak pressure slighlty.

What your gunsmith wants to do it make this angle less steep... more gently easing the bullet into the rifling and spreading out the pressure spike from engravment. What it will also do is lengthen the distance the bullet has to travel before being fully engraved.

Some examples:

The German specifications (1939) for the 8X57 usually uses a 17.2 Min. of anle taper. the typical us made 30-06 used one of 1 degree 22 minutes....why? The Gernams were using a lot of steel jacketed hunting ammo, we wre using typical jacketed ammo.


A quote for the British textbook of Small Arms (1929):

"the shorter this free travel and the steeper the angle, the greater the resistance to forward motion and the quicker and higher the gas pressure rises."

Personally, I'd not bother to change it...through load "juggling" can find a cast bulelt load that shoots well in the standard barrel....and if you can't find it after exhasutive searcing and testing, then think about changing.

Thnks...got lucky with this one.

Don't think I got eveything I wanted to get across clear. By changing the angle of the rifling's origin, it could make the rifle shoot better...but it proably will make it shoot better with bullets of longer bearing area rather than all bullets. Given the OAL requirments for working through the magazine, may find that you need a differnt bullet than you were planning on using...one with less nose and more body. Don't have the option of seating a long nosed bullet farther out in teh case if you want it to cycle theough the action...so you may have to go with a shorter noced/longer body bullet to get that bullet snuggled up to the rifling.

That free bore area...the UNrifled part leading up to the tapered lands...is usually over bullet diameter. Made a bit large so that fouling and general "gunk" can accumulate and still have the rifle chamber ammo. Letting a bullet jump that section unguided isn't usually good for accuracy...and if at some point the bullet isn't BOTH guided by the case and by engravment, it's unguided...adn to do that with a longer taper means you need a bullet with a longer bearing area.

If we made the "free bore" section almost bullet diameter, accuracy wouldn't suffer so much from the jump....but it would clog up with fouling, refuse to accept ammo not carefully made, and generally be troublesome for a non-gunnut...so they make that area larger than it needs to be to keep complaints down.

An abrust start of rigling does riase pressure...and sometimes that can help. IF it raises pressure enough to help "slug up" a bullet slightly too small (And the bullet is sopft enough to deform), then it actually does some good.

AK-clones often have an very abrupt angle of rifiling...enough that I can get some of the softer .308" bullets to shoot well in the over sized bore. Besdt I can guess, the abrut angle right where pressure is at it's greatest helps slug up those bullets.