| Posted: Tue Jun 2nd, 2009 11:03 PM |
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Fiftydriver
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Well, I have been shooting the 22 K-Hornet and 218 Mashburn Bee for many years but I have always had a real problem fireforming a case that headspaces off the rim and that has a dramatic transformation in case design, namely shoulder location.
The reason is because these cases are extremely thin walled and any case stretching while fireforming can cause the cases to seperate within just a few firings with top loads.
In addition to that, I have always found that accuracy has never been overly impressive, sure fireforming loads make usible 100 yard varmint loads but you will have some misses thrown in there just because of variations.
I have tried the standard tricks such as seating the bullets solidly into the lands and to be honest, I have never found this to be a good method and did not improve accuracy. With the 22 K-Hornet, I always noticed that on some of the fireformed cases, the primer would be noticably protruding on some while not on others. Obviously this ment that that the cases were no where near the same consistancy as far as shoulder location. In essence, once you fireform the cases, you will have to shoot them again under high pressure loads to get the headspace measurements consistant, I never liked two fireforming loads......
Well, this morning I was able to get over to the shop early and had just gotten in a new batch of 22 Hornet cases so I decided to work on some new fireforming loads as my old cases are ready to be scrapped. I wanted a decent load accuracy wise for varmint hunting while fireforming. Started with the 40 gr speer SP over a decent load of H-110. Loaded up 4 just to check accuracy and went out behind the shop at 50 yards and touched them off. The four shot group was just under 1 1/2" ctc. Certainly not what I was looking for.
Went back into the shop and loaded 6 rounds using the 50 gr Blitzking and Lilgun. Overall group was pretty decent but still around an inch and total group size was just over 1 3/4" with one flier...... Here is a pic of those two groups:
The left group is the 40 gr Speer and the right is the 50 gr Blitzking load.
Looking at the cases, I could see that the primers were hanging well out of some of the brass and not on the others. I did not want to increase pressure because case stretching would become a problem.
I set there for a couple minutes and then grabbed a 6mm BR FL sizing die. One of those out out of the air ideas. Dry lubed the virgin 22 hornet case necks and expanded them to 6mm. Which made a pretty neat looking case as well but thats for another time.
I then ran the cases into my 22 K-Hornet just far enough so that they would chamber but with a bit of resistance telling me the case shoulders were solidly against the chamber shoulder. Here is a pic of the cases:
From left to right, virgin 22 Hornet, Hornet case necked up to 6mm and then back to 22 with shoulder located properly for the K-Hornet chamber and the finished fireformed 22 K-Hornet case.
I went back out and shot the 6 loads I had loaded up with the modified virgin cases. Again at 50 yards. By the way I was shooting off a BR harris bipod and rear sand bag.
I was expecting things to tighten up and they did. This group measured 0.460" ctc. Please excuse my fancy targets!!! Obviously it made a huge difference in accuracy. This rifle with its best loads with fireformed brass will get from 3/4 to 1" ctc at 100 yards so anything at 1/2" or less at 50 yards is certainly near the top performance of this rifle which is a Ruger M77/22H sporter with nothing other then a trigger job done to it.
Aside from the accuracy improvement, The primers were all very consistant and even with the case head so all cases were consistant in their shoulder location. I also wanted to check case wall thinning which has always been a problem with the K-Hornet and the Mashburn for that matter.
I used my RCBS case master to check the case wall thickness on the cases of the first two groups and these cases showed clear thinning just ahead the case head. In fact it was roughly 8 to 10 thou thinner then the virgin cases in the same area.
The cases that I had repositioned the case shoulder were then measured and they were also thinner but only by 2 to 3 thou so easly 3-4 times less case wall thinning from fireforming. Now adding this step does increase the time needed to make fireforming loads but not by much and the cases neck up so easily its hardly any trouble at all.
One potential problem could be neck work hardening with the potential of case neck splitting sooner then normal but this can be easily corrected with neck annealing if it does happen, case wall thinning just ahead of the case head can not be corrected in any way once it starts so I think it would be better to deal with neck hardening.
I will try this with the next batch of 218 Bee cases as well when I fireform some Mashburns and see if I get the same results which I am nearly positive I will.
I am also thinking hard about that 6mm Hornet or 6mm K-Hornet. Comparing same capacity cases, one in 22 and one in 6mm, the 6mm will generally offer 100 to 125 fps more velocity potential with same bullet weights and same pressures. I can get around 2800 fps with the 22 K-Hornet with the 55 gr Blitzking, a 55 gr tipped 6mm bullet at over 2900 fps would be pretty interesting and the larger diameter bullet would also "pop" small varmints with more authority, will have to think on that one. Maybe a 6mm Mashburn would be a better choice and add another 100 fps. To many projects to play with.....
Anyway, if your fireforming for the 22 K-Hornet or 218 Mashburn, this may help you get much longer case life and also offer much better accuracy from fireforming loads in your little wildcats.
Good Shooting,
Kirby(50)
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| Posted: Wed Jun 3rd, 2009 12:49 AM |
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72coupe
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I have read some reloaders notes from when the K Hornet was new. Thinning has always been a problem.
That is a good inventive solution.
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| Posted: Wed Jun 3rd, 2009 02:10 AM |
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Fiftydriver
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If you look at the pic of the fired case you can see that this chamber allows alot of case expansion because of its loose specs. I had this rifle rechambered long before I got into building rifles. I have time and again debated on getting in a match grade barrel, drawing up a true min spec reamer and doing this right.
The biggest problem with the 22 K-Hornet is that most use reamers that are far to loose in dimension that allow the case to expand to much, come to think of it, this is the problem with most of our rifle chambers.....
Kirby (50)
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| Posted: Wed Jun 3rd, 2009 03:28 AM |
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Rockydog
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Kirby, I think you are right on with your chamber comment. I've been struggling with my latest acquisition in 6TCU. Set the shoulder back too far and ended up doing almost exactly by accident what you did on purpose. The 6mm cases were so long on headspace that they were separating. Not wanting to waste them I renecked the 6 TCU cases back to .223 by necking down bit by bit until I achieved a crush fit in my 223 bolt gun. I've loaded with .223 bullets and now will blow the shoulders back to 223 dimensions and leave these as .223 and start over making 6mm with other cases. As to your chamber comment. I was going to neck size by backing my FL die back a 1/4 turn or so but the 6mm TCU cases are so large after firing that I can barely get them in the die and end up basically FL resizing anyway. These things are tight in the Hornady die! Maybe it's just the straighter case wall than I'm used to but the chamber sure seems large compared to the die. RD
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| Posted: Wed Jun 3rd, 2009 03:48 AM |
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Fiftydriver
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Yes that can be a real problem.
I have drawn custom reamer prints for over 60 reamers and half of them have been for factory chamberings. I draw them up to be made to min spec but not out of SAAMI specs, just minimum.
Problem I have ran into many, many times is that the factory FL dies will not size the fired cases down at all because the standards have become so lax in the industry. On top of that, most factory dies will not allow you to bump the shoulder on cases fired in many of my custom chambers because they are so loose in spec.
It is not that my chambers are undersized, they are drawn up right off the SAAMI spec sheets, die makers are just that slopy and so are the firearm manufacturers and their chamber sizes. Really sad, and to be honest a pain in the rear.
ON several occasions, I have had to had custom dies made or order in new reamers if customers wanted to use commerical loading dies. TO correct the length issue for bumping the shoulder, I simply use a carbide cutter and take 20 thou off the base of the die which will allow the die to FL size the case and bump the shoulder if needed.
It can be a real mess. What your seeing with your 6mm is really not that unusual. THe real problem is that your brass is getting work hardened doing this. Be careful and watch for case head seperations on your cases.
Kirby (50)
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| Posted: Wed Jun 3rd, 2009 04:14 AM |
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Rockydog
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Kirby, I've annealed all the cases prior to fireforming but I never got that far. On my second trip to the range for fireforming I had a head separate and had about 15 cases with distinct separation lines starting (everything I'd fired prior to the separation). Trashed them all and renecked about 200 cases to form back to .223.
Then I backed my 6mm die out to reform the neck but not touch the shoulder. Since it's a Contender I now have to snap about every third case into the gun but I don't think I'll have headspace problems.
Since you have the reamer made to your spec, have you ever cut your own dies using the chamber reamer? Is polishing the dies a problem? RD
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| Posted: Wed Jun 3rd, 2009 06:21 PM |
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Fiftydriver
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I make seater dies all the time with the chambering reamer. Obviously the sizing dies would not work with the chambering reamer as the die needs to be smaller then the rifle chamber to resize brass.
I have not gotten into making custom sizing dies yet.
The TCs are kind of a pain when fireforming because they do not function well with a crush fitted case which most improved case designes need for proper fireforming. They certainly can be frustrating. I bet if you had it to do over you would probably opt for the standard 6mm-223 or 6mm-222 Rem Mag!!!
Good Shooting!!
Kirby(50)
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| Posted: Thu Jun 4th, 2009 02:05 AM |
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Rockydog
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Kirby, I was actually looking for a 6/.223 when I stumbled across this barrel, forend and dies for about 40% of new. I might know why they were sold. Definitely a challenge. RD
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| Posted: Sat Jun 6th, 2009 10:58 PM |
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Katch1
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I shoot the k-hornet also, but so far have yet to see the accuracy problems you have, but the splitting problem I have. The necking up idea is a good one, my .19 calhoon has less of all the problems than the .22. Have you tried a slower powder? I use a1680 in all my hornet class loads, and have good luck with it. I also shoot 42 gr or less bullets?
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rat31465
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Fiftydriver wrote: I have tried the standard tricks such as seating the bullets solidly into the lands and to be honest, I have never found this to be a good method and did not improve accuracy.
The only real purpose for seating the bullet into the lands for fireforming a rimmed casing is to square up the cartridge in the chamber. That way when you fire the round you are less likely to end up with a bad casing.
I may be stating the obvious here as I haven't ever owned a Rimmed wildcat which required fireforming, Just Rimless.
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