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Author
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Topic: excessive pressure
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 25, 2004 04:26 PM
I am in the process of working up a load for my tac 20. It is a new cartridge for me and I have had to rely on what I have read about others loads.
I was anywhere from .4 grains to 1 full grain below what I had read was maximum. I had approached this load slowly. Yesterday I would shoot 3 to 4 rounds and then suddenly blow a primer. Happened about 8 times in the twenty I shot. Other rounds showed slight dimpling at the primer and one or two showed the tell-tale bright spot on the head from the extractor. Some rounds showed no sign of pressure.
Each charge was weighed. To me, this is a big difference in pressure between rounds. It goes without saying I intend to back off from this charge weight.
Would like to know if there could be any other reasons for such drastic differences in pressure other than charge weight. I believed I was below maximum and had reached this point with no signs of pressure.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
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Tim Behle
Administrator MacNeal Sector
Member # 209
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posted October 25, 2004 06:02 PM
What kind of primers are you using? I've not reloaded for a 20 cal, but I only use the Remington 7 1/2 primers in my 17's due to the hardness of the primer cup. Other primers won't hold up to the pressure that the round creates.
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Personally, I carry a gun because I'm too young to die and too old to take
an ass kickin'.
Posts: 3160 | From: Five Miles East of Vic, AZ | Registered: Jun 2003
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 25, 2004 06:43 PM
Tim,
I was using Rem 7 1/2 primer too. I had increased the charge by .3 when all this happened. And what is really strange, the bolt lifted very easy and all were ejected with no problems.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
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Tim Behle
Administrator MacNeal Sector
Member # 209
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posted October 25, 2004 07:17 PM
Who made your barrel? It is possible that you have either a tight barrel, or even a tight spot in your barrel.
With one load in my 17 Rem. I can't use the Hornady book max with Hornady bullets. They blow the primers. But I can use that same load with Berger bullets of the same weight. You might try a different brand of bullet.
My hunting load is only .4 under a load that blows every third primer. Each barrel has it's own limits, yours might have lower limits than the test barrel they used to write the book.
How does it look over the Chronograph? Are the numbers up where you want them? Does it group well?
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Personally, I carry a gun because I'm too young to die and too old to take
an ass kickin'.
Posts: 3160 | From: Five Miles East of Vic, AZ | Registered: Jun 2003
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 25, 2004 07:30 PM
Tim,
The bullets are 35 gr. Berger. The rifle is a Cooper. Chronograph at 4260. I wanted to be around the 4200 fps mark. I have exceeded my expectations there. I would not mind if it was 100 to 150 fps. slower. The groups were great. Proverbial dime sized. Might have done better if I wasn't getting hit in the face with blow back every little bit.
I really don't want to switch bullets. And I don't mid reducing the loads , I will still be where I want to be. Just curious as to why? Your experience shows me a little can mean a lot with the sub calibers.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
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Tim Behle
Administrator MacNeal Sector
Member # 209
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posted October 25, 2004 07:50 PM
I'd try backing off .2-.3 and see if they still blew primers, hit accurately and were close to the speed you wanted.
When I do load development, especially with my 17, I always wear safety glasses and I have a piece of leather ( A doe skin ) that I lay over the back of the bolt.
I've burned my cheek more times than I care to remember, and that doe skin stops most all of the blow back.
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Personally, I carry a gun because I'm too young to die and too old to take
an ass kickin'.
Posts: 3160 | From: Five Miles East of Vic, AZ | Registered: Jun 2003
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Leonard
HMFIC
Member # 2
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posted October 25, 2004 08:00 PM
One thing you should look at is the possibility that the firing pin is too long, or too thin. Does the indent appear to be about normal? If this is the case, stoning it slightly is a simple solution, if you are mechanical and handy.
Other than that, it could be your sizing, if you are using lube as you neck the case to twenty caliber. In other words, there may be too much neck tension, maybe you can even see a slight ring of copper, after seating a bullet?
The other possibility is simple; too hot of a load.....in your gun.
I wouldn't advise you to (again) fire 20 rounds with 8 pierced primers before investigating the situation. This is a serious situation and can damage the bolt head, even if it is not enough to shear the lugs or send hot gas in the shooter's direction. One pierced primer, regardless of the condition of the fired brass on those that did not pierce, is cause for concern. Especially since you are weighing charges. A published load is only a rough guideline. Ambient temperatures play a part, and firing a string in a hot barrel increases the pressure, as well.
In short, there are many things to look at. Don't take it lightly.
Good luck, LB
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EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32361 | From: Upland, CA | Registered: Jan 2003
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Jack Roberts
unknown comic
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posted October 25, 2004 10:41 PM
Apparently even a strong hint doesn't get your attention. Keep it up and you will be picking powder and brass pieces out of your face. Hope you are wearing glasses, because picking pieces out of your eyes is a lot more expensive. You will have to pay a professional to do that.
There is a large tolerance in SAAMI chambers. A published load is usually safe in the mid sized chamber but dangerous in the small sized chamber.
Pressures in those small chambers peak rapidly and unexpecedly with some powders.
Jack
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 26, 2004 04:17 AM
I fully admit it was stupid on my part. I was just bewildered at the time.Shoot 3 to 4 with not a hint of pressure and then suddenly it would happen with all charges equal.
I always wear shooting glasses. Although from my post it may not sound like it, I have been handloading for a long time and I don't intend a repeat performance of the situation I described.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
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Leonard
HMFIC
Member # 2
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posted October 26, 2004 09:26 AM
Randy, don't take it personal. You are to be congratulated for posting the question and risking potential abuse. It's not mean spirited, but you know how it is, gotta go with what is written, and assume nothing.
Jack is right about pressure peaks in small volume cases. I heard once, that the single caliber most responsible for blowing up Model 700's is the dimunitive 17 Remington; not the elephant guns.
I just hope we have given you something to work with, wish it could be more?
Good luck, LB
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EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32361 | From: Upland, CA | Registered: Jan 2003
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DAA
Utah/Promoted WESTERN REGIONAL Hunt Director
Member # 11
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posted October 26, 2004 09:37 AM
Blanked primers without any other indication of pressure. I'd be for making sure those cases don't have excessive headspace!
- DAA
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"Oh yeah, they're gonna talk to you, and talk to you, and talk to you about individual freedom, but they see a free individual, it's gonna scare 'em." -- George Hanson, Easy Rider, 1969.
Rocky Mountain Varmint Hunter
Posts: 2676 | From: Salt Lake City, UT | Registered: Jan 2003
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Leonard
HMFIC
Member # 2
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posted October 26, 2004 10:17 AM
Good point, Dave.
I thought about it in both of my responses, but it slipped my mind, at the last minute. I was hoping we would hear from you!
Good hunting. LB
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EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32361 | From: Upland, CA | Registered: Jan 2003
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 26, 2004 12:11 PM
Leonard,
I have never been one to try and impress people with my knowledge or in some cases the lack of it. Never been afraid to ask questions either.
In this case, any abuse would not only be well founded, but expected.
I am investigating the head space question. I will post a reply with my findings. I did go back to my starting point and found velocities to be 100 fps slower than when I started. No blown primers, but I did see the shiny spot on one case. The cases I have been shooting were prepped by the person I bought the rifle from. I will now do my own.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
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DAA
Utah/Promoted WESTERN REGIONAL Hunt Director
Member # 11
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posted October 26, 2004 12:38 PM
The headspace issue is just a possible explanation for what you are seeing. Without "being there", or having more info, I'm just guessing. Tim and Leonard have both brought up good points that need to be taken into consideration. I just noticed that nobody had mentioned headspace yet though, and in my experience it is a common cause for blanked primers as you describe. ESPECIALLY when dealing with die formed wildcats. Going from memory, I can't remember whether you move the shoulder around when forming T20's or not, so it may not be as likely here as I'm suspecting. If I were forming them, I'd just neck down for a false shoulder and hope it would hold headspace. I know that with cases like the .17 Mach IV, just simply following the directions that come with the forming dies (i.e. screw them down to touch the shell holder) will OFTEN create excess headspace. Seen it many times.
Like I said though, may or may not be what you are dealing with. Easy to check though.
- DAA
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"Oh yeah, they're gonna talk to you, and talk to you, and talk to you about individual freedom, but they see a free individual, it's gonna scare 'em." -- George Hanson, Easy Rider, 1969.
Rocky Mountain Varmint Hunter
Posts: 2676 | From: Salt Lake City, UT | Registered: Jan 2003
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R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
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posted October 26, 2004 01:43 PM
My loads had been used with the brass that came with gun. The brass had been resized,deprimed, and chamfered. All looked good. And then enter the problem. After reading everyones suggestions, I went back to square one. Resized the once fired brass by checking headspace and lowering the die as needed. The bolt just felt snug when closing. Began at my original starting point. No signs of pressure and velocities where back to normal. I have now increased the charge to within .5 grains of the blown primer load. Absolutely no signs of pressure. Used thumbnail across the primer and felt nothing but smoothness. No shiny spots from extractor either.
Ran out of time today, but I intend to approach the load where I had problems. I still believe that I will be at least .5 grains below maximum. However, it will only take one blown primer this time. I think the problem was with the headspace created by resizing. Thanks to everyone who posted.
Randy
[ October 26, 2004, 03:24 PM: Message edited by: R.Shaw ]
Posts: 567 | From: Nebraska | Registered: Jan 2003
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Leonard
HMFIC
Member # 2
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posted October 27, 2004 10:37 AM
Well, maybe you have a solution?
At this point, using the already fireformed brass, you have a different situation, entirely. That's (if) the case forming was part of the problem?
Be sure and check back with some terminal performance, on live targets.
Good luck, LB
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EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32361 | From: Upland, CA | Registered: Jan 2003
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Cal Taylor
Knows what it's all about
Member # 199
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posted October 27, 2004 05:44 PM
One more possible, but unlikely problem. Since you don't actually know what the history of the brass is, some may be longer that others. And if it gets too long, when you seat your bullets, you get a crimping effect which creates higher pressure in some than others. That may explain the variances from round to round. Just a thought.
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Democracy is two wolves and a lamb deciding what to have for lunch.
Liberty is a well armed lamb contesting the vote.
FoxPro Field Staff Member
Posts: 1069 | From: Wyoming | Registered: May 2003
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5shots
Knows what it's all about
Member # 427
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posted October 29, 2004 11:17 PM
i once had the same problem even light loads didn't work though, it turned out to be a very tight neck in the chamber, shaved .001 in from the chamber neck area and problem cured with no loss of accuracy
Posts: 28 | From: glendive,mt | Registered: Oct 2004
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Leonard
HMFIC
Member # 2
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posted October 31, 2004 12:13 PM
Welcome to the New Huntmasters, 5shots. Glad to have you on board.
Somehow, I missed your post for a couple days?
Good hunting. LB
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EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32361 | From: Upland, CA | Registered: Jan 2003
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