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So if I have this correct, as the barrel's dimensions are eroded in the throat and leade that the precision of the firearm drops.
As the dimensions of the barrel erode where the case's shoulder and neck are supported, the reliability is reduced, as now the case will be seating farther into the barrel, and the case will be obturating to larger diameters to seal system and let the pressure push the bullet forward.
Correct.
These areas generally do NOT erode because they are not in direct contact with the heat and friction (powder/gas) that the throat and leade are.As the dimensions of the barrel erode where the case's shoulder and neck are supported, the reliability is reduced, as now the case will be seating farther into the barrel, and the case will be obturating to larger diameters to seal system and let the pressure push the bullet forward.
The brass cartridge casing acts as a gasket to the high pressure and also protects the actual chamber body, shoulder and neck from erosion.
If the chamber body, shoulder and neck are wearing, it's from the abrasive properties of dirty ammo.
So when do you quit re-barreling and just replace the upper? I've heard 20,000 rounds?![]()
Randall,
Ok...my apologies for not looking at the tacks in your threads/ My Bad, and it did totally answer the concerns I have. Which are....
1. Throat erosion does not come into play as far as safety and reliability because the shoulder creates the head space dimension and rarely wears like a throat does. (I knew this, but wanted confirmation because of some of the other posts that said the cartridge could go deeper into the chamber if the throat is worn.)
2. The "Field Gauge" is the one to have to measure acceptable head space limits. If the bolt closes on the "Field Gauge", change the bolt. If it closes on the new bolt...change the barrel. The "GO, and "No-GO Gauges are used primarily for new barrels to check head space after reaming.
3. There is no way to ascertain how long a certain bolt or barrel will last, (some say 10,000 rounds, others say 15,000 to 20,000 rounds) but best to check head space with the "Field Gauge" every 3,000 rounds or so.
That's a "Wrap" for me. Thanks for the education.
Tack
I would think this depends on the quality and type of upper you have. When you think about it, what actually wears out on the upper itself? (Other than the components of the upper, bolt, Cam Pin, Gas Rings etc.) I've checked the Uppers race way, dust cover, forward assist, and the pivot pin lugs, and do not see ANY wear after 6400 rounds.
I have an MRP upper, and switching barrels is a snap without gun smithing tools. The Gas tube and Gas Block are an integral part of that barrel setup. I would think I could re-barrel that upper forever.
My standard M4gery upper is a bit different, and would need an armorer to do the barrel, gas block and gas tube change, because i don't have the tools or knowledge of how to do this. In this instance I might just decide on skipping the hassle and buying a new upper, and saving the old one for a "Fence Post".
Tack
One order for a field gage out to Brownells today.
As much as it pains me to admit it, 3,000 rds is about a year's worth of shooting for me. So I don't see a problem in doing a minor overhaul on at least an annual basis. Of course...
All I gotta say is that guys these days are sure fortunate to have better choices out there and are able to afford it.
I built my first CAR-15 back in 1980. No shit parts gun bought at several tables at a Dallas gunshow. Cost me about $400.00 and some change. SGW lower as I recall, various other vendors (like I knew who anybody was back then). It ran like shit at first. Took a awhile to upgrade parts and get it running right. I ran it in the reserves for several years, running a shit-load of blanks through it, and the occasional live fire. After each year it was pretty much trashed and needed re-building.
Down through the years I have built several more carbines, as I learned of new vendors, and my wallet could stand it. I ran Bushys for quite awhile through the 90's, thinking they were the best game in town.
Through all this I admit my thinking may be skewed because of my experiences with marginal parts, but these things do wear out, even with the best of parts.
Recently, I have totally re-built my carbines, taking advantage of the M-4 program, and the incredible amount of private sector work that has been done to improve this design, and make it available to the general public. You guys are incredibly lucky that you can now buy a state of the art carbine that in many ways can exceed the mil spec. Twenty seven years ago this was not the case. Even if you could afford a Colt, you still had problems with carbine length bbls.
So I hope you guys are right. It would be nice to get 15-20K rounds through my new builds without much parts replacement. Only one way to find out.
Tactical nylon gear maker.
Diz, You have twisted my arm! my next barrel will be a mid-length. Possibly a RRA unless someone can suggest a better choice.
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