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Smooth Chambers
@ 08:30 pm (GMT) |
Mike NeesonHi, hopefully I'm not turning over old ground here, but I was lead to believe - schooled in fact - by my gunsmith, that the case needs to be totally free of all traces of lube so that it grips the wall of the chamber on firing. He explained that if the case did not grip, the bolt face could experience more thrust than desirable. Now I know that lube in the chamber is bad - particularly in the regard of causing bulges, but the below modelling by an engineer(?) seems to demonstrate that the smoother the case and chamber, the better. Leading to reduced thrust on the bolt and better case life. Have a read and see what you think. I'd be interested to hear everyone's thoughts.http://www.varmintal.com/a243zold.htm |
Replies
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@ 03:26 pm (GMT) |
Mike NeesonRe: Smooth ChambersYes Martin It's a Lee. It's nicely polished now and mates wonderfully with the die. Nothing like a good mating eh? |
@ 09:28 am (GMT) |
Martin TaylorRe: Smooth ChambersYeah...........I have had basically the same problem before with Lee holders years ago but had forgotten all about it. l didn't use the same shell holder all the time when F/L sizing (rookie mistake!!) and the Lee had a few thou difference compared to the Redding or RCBS that l have. Drove me mad as a new Reloader (& Nathan!!!), all of a sudden my 243 & 06 had tight chambering issues on and off. I spend a lot of time setting my F/L dies to bump just the right amount to suit that chamber. Now all the matching bases are set on the same holders so it can't happen again. Have fun!! |
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@ 12:49 pm (GMT) |
Mike NeesonRe: Smooth ChambersUpdate. Been out to fireform and do a preliminary load testing and it's like I'm shooting a completely different rifle. Nodes and groups are more consistent, hints of ultra good groups followed by increasing then decreasing then back to hints of excellent accuracy. I say hints because I'm out of practice. 2 rounds on top of each other and a flyer... but much more predictable. Also have been able to up the load without pressure signs too. Originally my load of choice was 43.5g 2206h with anything above that being problematic, I've now tested up to 44.5, no pressure and appears to be an excellent node too - once I get my mojo back. Extraction has been excellent throughout. I'm stoked. Photo cause it makes me happy.
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@ 01:34 pm (GMT) |
Mike NeesonRe: Smooth ChambersUPDATE: Grant, you were right. I have noticed concentric rings on the fired brass (easily seen on the clean brass) so will go and get someone to pull the barrel and polish it for me.Questions for the brains trust. I was at the range last week and shot 30 rounds over my F1 Chrony through a clean barrel - load was 44.5 2206h, Fed210, 168AMAX COAL 71mm and the first few strings of 3 rounds after a couple of foulers, showed about 2750fps with quite a large ES ~30fps. As I continued shooting (controlled tempo, stopping when barrel was only warm) the velocity slowly increased up to 2800 fps with an ES of 6 fps! Groups were great (half inch or there abouts at 200m) and pressure had increased causing extraction to become a little sticky - no primer flow to be concerned about. I hope the extraction can be sorted by getting the chamber finished properly. 20 degree day, overcast with chrony under a high tin shed roof Barrel seems to be a slow fouler. Question 1: What is happening here to have the pressure and velocity increase? Question 2: (Ignoring the slightly sticky extraction) Can I replicate this pressure by seating the projectile a little deeper? Question 3: Should I clean the bore less? I clean it post every shoot. |
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@ 09:16 am (GMT) |
Martin TaylorRe: Smooth ChambersI wouldn't read to much into this chamber Mike until it's sorted that's not a hot load.With the cleaning, now that it's run in l would only clean when fouled as per Nathan's examples in your book. Have seen many barrels carm down after 5 shots or so. |
@ 09:28 am (GMT) |
Grant LovelockRe: Smooth ChambersHey Mike, I gotta show this to the missus..... "Grant your right" I told her its possible shes not the one whose right ALL the time.... lolNow if I could only get her to say those words...... |
@ 03:09 pm (GMT) |
mark whiteleyRe: Smooth ChambersMike I'll have a crack at answering for you,Nathan explains quote, from a clean copper free barrel, the first shot will often be way off from the normal grouping, called a fouling shot. this shot puts a layer of copper onto the inside of the barrel and the next shot will likely gain about 50fps in velocity. after about 150 to 200 rounds, the problem will re-occur, this time to too much copper fouling. http://www.ballisticstudies.com/Knowledgebase/Basic+Rifle+Accuracy+and+Ballistics.html I have seen this to be true but I'm not sure if this fouling would be enough to send your pressures up I put your load into quickload for a look it came up with 68334psi, 2838fps there are a lot of things in a load that need to be tweaked before getting more exact figures from quickload and it is a prediction only but quickload is saying your load is way to hot and that your max would be about 43gr of 2206h for 61568psi and 2758fps this is about the same velocity that adi has and is max at 43gr 2206h seating the bullet deeper to 70mm puts the psi at 63692psi and 2774fps as far as cleaning goes, IMO if you are using your rifle regularly then after use patch some inox through and patch out to preserve, if you are storing clean thoroughly there is a thing getting about called copper equilibrium or something I don't know that much about it and I'm not sure about it my rifle's don't take more than one shot to foul and usually at the start of the season I will check the rifle sight and use it I know you understand Mike that what is ok in one rifle may not be in another so if someone else can put more powder in don't mean you can but IMO as you have got the rifle to shoot you will again you need to find the lower node mate;) regards mark |
@ 04:52 pm (GMT) |
Nathan FosterRe: Smooth ChambersOk, in your TF barrel, I would expect that its perhaps a low fouler. So as others have said, it will only need copper removal once in a while.It may just be that your perception of "warm" changed over the course of the day in a relative manner. The day gets hotter, the barrel still only feels warm, but relative to the environment. It could actually be hotter than when you started, this effecting velocity due to changes in the steel as opposed to major changes in the powder, though this will occur to some extent, regardless of any attempt to build in stability. If was to guess the cause and based on the assumption that copper fouling is low, I would say that carbon fouling is having an effect. If the copper build up is low, you may find that with carbon fouling, this is the barrel's norm. If you clean the rifle heavily, you will lose this norm. These things are always hard to determine via the internet. Your barrel is from the same batch as my current barrel. These do appear to like 44gr- depending on individual chamber specs. Mine produces extremely low copper fouling but needs several shots to get its carbon layer up if I strip it back. I am currently using the slow fouling cleaning regime as outlined in my Accurizing book, second ed, 2015. The rifle is seldom cleaned until I am forced to, not by poor accuracy as this rifle is a continual one hole grouper, but instead when I need to polish and preserve the throat as a part of ongoing maintenance. 2800fps is a bit steep for maximum case life in a shorter barreled .308. It might need to be downloaded slightly. But again, do not clean it just yet. Wait until the throat needs a pick me up. Yes, I have seen the copper equilibrium thing. Another buzz word to try and put a subject into a one size fits all box. It is on the right track, however the method lacks an in depth understanding or explanation of all relevant factors. |
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@ 11:02 pm (GMT) |
Mike NeesonRe: Smooth ChambersThanks all for your help. Looks like the 2nd edition has the gold I need. I'll back off the load a little and see how it goes from there. My load development is currently tempered by rusty technique, so a few do-overs will be called for and help cement things. Progress is definitely being made and things are really coming together. Learning so much. So again, thanks to all that have been following this and offering some well thought out advice. It is very much appreciated. |
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