guide gun chambers

[simplicity]

I just recently picked up a used stainless guide gun in 45-70 and have been playing with loads for it and with certain loads mostly just going past the medium loading data on the hodgon site I get some case buldge  If I go beyond 52.5 grains of Imr 3031 under a speer 400 grainer. (it's giving me 1780 fps with 52gr. and it drops back to 1700 with 52.5) I get alot of expantion just above the rim about where the die stops during resigning. My question is do the chambers in the guide guns or 1895's in general run a bit on the big side?  I can understand them makeing them on the large side for well reliability when facing something mean and fury hence the reason for the guide gun model.  I'm just trying to figure out if this is the norm or I just have one with a big chamber. The cases with the exspansion still will chamber after firing with no problem and there is no problem extrating them. I just think if I tryed the buffalo bore rounds  I don't wanna have to worry about head separation. Also what's Marlins policy on someoen haveing a used gun with if it is a factory defect. I know this is probly sounding a bit unclear but any help or info would be great thanks.

[john keyes]

the hottest rounds I have fired is 49.0 H 322, Rem 405 at 1703 from a ported guide gun with a 18.5?" barrel...

most of the others were a little milder with H4895.

to answer your question no, I have never noticed any bulging or reshaping of the brass after firing. 

about the only time I have seen that was some 10mm hornady ammo after firing and that was supposed to be normal.

[Ridgerunner665]

What the OP is seeing is PRE (pressure ring expansion)...

 It is normal with warmer loads and generous chamber dimensions. My load is 50 grains of H322 under a Beartooth 405 LFN/GC in Remington brass (1,886 fps from a 22" barrel) and I get .006" of PRE.

 PRE does not mean excessive pressure...it is pretty much useless for trying to figure pressure unless it is compared to a known pressure tested load.

[Bigeasy]

Case head expansion is normal in any rifle.  It varies with the type of action, chamber dimensions, make of brass, and load being used.  Lever actions tend to show slightly more due to rear locking / action stretch during firing.  Marlin does not chamber its rifles with over sized chambers. Question is what is excessive?  Excessive usually means a hot load, or less common, and oversize chamber / excessive headspace.  Don't want to quote exact numbers as I am not as up on it as I should be.  I would run a go / no gauge thru the gun to ensure correct headspace, then I would measure the case head expansion of several factory loads that are similar to your reload.  If there is a notable difference, back it down a grain or two.  If you are concerned with an over sized chamber, have a gunsmith make a cast of the rifles chamber, and measure it for proper dimensions.

Larry

[Ridgerunner665]

PRE and case head expansion are 2 different things...

[Bigeasy]

I do believe that case head expansion is the same as PRE.  You are measuring the expansion of the brass against a known load and pressure to determine signs of high pressure.


From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: Re: "HIGH-PWR" Loads, Waters method

"Here is an update on the Waters method calculations.
To review, the Waters method measures the "pressure ring" diameter
just behind the case head to tell when the pressure of a load becomes
excessive.   The theory was that when this diameter stops growing or reaches
a .5 mil increase over moderate loads, that it signals that the pressure
is getting too high."


Larry

[Ridgerunner665]

Case head expansion expands the primer pocket, rim, extractor groove, and the web area of the case.


PRE expands the area above the web, with no expansion of the case head.

From the way that is written...Waters measured the web, PRE occurs on up the brass and is quite common in warm loads in straight cases  that were formerly black powder rounds.   (45-70, 45 Colt)

[Bigeasy]

I won't argue the point then.  My original answer to the OP, I believe, remains valid.

Larry

[Ridgerunner665]

My load mentioned above is 38,000 psi per QuickLoad...well within spec for a Marlin.

[Ridgerunner665]

I'm not arguing with you friend...just stating my experience 

[simplicity]

Thanks ridgerunner That pretty mus is what I'm getting for exspansion on the case .006,  I have a good load with 400's at 1780 fps no PRE noticable, if I go another two grains it's noticable and according to the chrono only another 20 fps added so I went back to the 1780 fps load (18.5" barrel) Thanks again for the replys

[Ridgerunner665]

You're welcome...

If you do decide you want a bit more...a slower powder (H322) will get you there within safe pressure limits.


006"-.007" seems to be the norm for PRE in Marlin 1895's with loads in the 38-40,000 psi range. They do have generous chamber specs...but it does not seem to bother accuracy.

My load mentioned above @ 100 yards...(only 4 shots because I ran out of ammo)






And since I'm new here...I'll show off one of my 1895's

[dpe.ahoy]

Nice group, nice gun and welcome to GBO!  DP