Full Auto vs. Semi Auto Bolts

chrisward3

chrisward3

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K guys, whats the difference?

(and do not tell me its the difference between full and semi auto...thanks:D)

i just picked up a LMT with s/a bolt (10.5" barrel) and just wondering whats the difference between the two. ive heard weight is one thing, but given that my gun will never be ran full auto, why would someone bother buying a F/A bolt?
 
The added weight will act like H / H2 buffer, softening recoil and reducing wear when using heavy loads.
On the other hand if you shoot light commercial load like Wolf, you might have short-recoil FTE/FTF.

It think the shorter the gas system, the more important it is because of increased gas pressure.

My .02, others can probably be more accurate.
 
chrisward3 said:
so then why would a 10.5" rifle package be sold with a S/A bolt where every other upper ive bought came with a F/A bolt?
Click to expand...

Because the American BATFE feel that any full auto parts in an AR-15 is constructive possession of a full auto. Up here, it's not that big an issue.
 
My understanding is that both bolts are identical, but there is one extra machining cut on the underside of the bolt carrier to allow for one of the F/A trigger mechanism parts to slide thru it. How does it get more mass ? My guess is an F/A bolt carrier probably is a hair or two longer overall.
 
chrisward3 said:
so then why would a 10.5" rifle package be sold with a S/A bolt where every other upper ive bought came with a F/A bolt?
Click to expand...

The rifle package you purchased was NOT built and sold by LMT... at least not as a 10.5" rifle package. It was bought by a dealer as separate components (lower, upper, Bolt Carrier Group, charging handle, etc.) and "assembled" by that dealer after the fact. Unlike LMT rifle packages it was not assembled and test fired at the LMT factory... it did not come with an LMT rifle package box, manual, etc..

The dealer you purchased from built the gun or they bought it from another dealer who built it... it did not come from LMT that way. Assuming they used LMT parts and properly verified headspace on the upper and BCG, then there should be no problem using an LMT S/A BCG with an LMT 10.5" upper. We have used S/A BCG's in the 10.5" with no problems as long as everything is done properly.

There is marginal difference between LMT s/a and f/a BCG's... I wouldn't get too concerned over it one way or the other... really not that big a deal.

The biggest issue might be selling it later... the majority of buyers want an F/A BCG in their 10.5" LMT's (that's how we package our LMT-STD105") so you may have to wait a little longer for a buyer but otherwise nothing to be concerned about.

Mark
 
Thanks Mark for the insight!

here's what i found ref: the post below about tripping the full-auto sear:

ht tp://www.olyarms.com/index.php?Itemid=42&id=29&option=com_content&task=view
 
Don't want to step on anybody's toes.
But accurate info and rumor control is useful:
So called FA (heavy) BCG are completely legal ( over the counter , if you will -- no NFA of 1934 paperwork needed ) down here in the states.
We have two in the house right now. They were on back order -- direct from LMT -- for months during the Great Panic .
 
Carriers are the same length... here is the difference for those that don't know...

bolt_carriers_bottom.jpg


They are NOT hard to get... we have lots of LMT Semi-Auto and Full-Auto BCG's in stock and listed on our website...

Mark
 
Thanks Questar, that what I remembered. But since I don't own anything "restricted", and as a result have never taken an AR appart (even less so a F/A specimen), a picture is worth a thousand words.

Questar said:
Carriers are the same length... here is the difference for those that don't know...

bolt_carriers_bottom.jpg


They are NOT hard to get... we have lots of LMT Semi-Auto and Full-Auto BCG's in stock and listed on our website...

Mark
Click to expand...
 
The Great Panic is pretty much over down here. I was glad to see it go. Prices had gone crazy and supplies of some ammo , guns , and even parts just dried up. The funny thing was that the prices on the lower quality quality EBR's and parts went up first & fastest -- LMT and the other pro grade stuff lagged behind -- a little , for a while.
It's a buyer's market for EBR's down here now.
 
chrisward3 said:
so whats the advantage to having an S/A bolt over F/A?
Click to expand...

S/A might be more reliable in a shorty with 55gr. commercial ammo.

My shorty with an S/A bolt and a Heavy buffer ran fine with 69 gr. milspec but short stroked with the lightweight stuff. - To much mass not enough gas.

A lighter buffer didnt work either - (not enough mass in the buffer for reliable chambering).

A lighter buffer spring with the H buffer cured it for 55's.

When I can afford SS109's I just put the normal spring back.
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My Colt semi auto carrier chewed up the buffer pretty good before it broke in. I have heard but can't confirm that a full round carrier is easier on the buffer, It does make sense though as it has more contact area.
 
There's no difference except a FA carrier will trip the sear on a select fire gun. Get either one.
 
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