View Full Version : Substituting FAL bolt carriers?

June 23, 2007, 13:12
Since the relationship between the bolt and the locking shoulder determine correct headspace, can you substitute carriers with out having to re-headspace? Also, if you can, are there any problems with using an inch carrier and a metric bolt? Sand cuts look cool but not cool enough to re-headspace. ;)

Mosin Guy
June 23, 2007, 13:18
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June 23, 2007, 13:30
Originally posted by Radio

Bottom line: ALWAYS re-check headspace when changing something!!

I understand the perplexity of those who claim the carrier should not affect headspace. Theoretically, the bolt will go as far forward as the round will allow, and drop with a certain clearance in front of the locking shoulder. Period.

I and others who have actually MEASURED know this is strangely not entirely true. I discovered there was OFTEN NO CHANGE, but SOMETIMES there was a SLIGHT change. I can only attribute this to:
* the unique relationship that any two parts will have due to wear and machining tolerances, or:
* various versions of these parts in use as detailed by Ted.

Here are my test results again, from March 14, 2001. I took painstakingly careful measurements, then performed the entire series a second time to double-check my readings. They were the same. Five of my seven bolt/carriers were from numbers-matching kits.I’ve broken this down into two sections for your convenience, first by bolt (“1” thru “7”) and then by carrier (“A” thru “G”). The bolts:

Bolt-1 is StG/Austrian, “Excellent”, matches Carrier-A.
A-259 B-259 C-259 D-260 E-259 F-259 G-259
Bolt-2 is StG/Belgian, “Very Good”, matches Carrier-B.
A-260 B-260 C-260 D-261 E-260 F-260 G-260
Bolt-3 is South African, “Good”, matches Carrier-C.
A-259 B-259 C-259 D-259 E-259 F-259 G-259
Bolt-4 is South African, “Good”, matches Carrier-D.
A-260 B-261 C-261 D-261 E-260 F-260 G-260
Bolt-5 is South African, “Good”, matches Carrier-E.
A-260 B-260 C-261 D-261 E-260 F-260 G-261
Bolt-6 is Belgian, “Excellent/New” (entire FP is black except for very tip).
A-261 B-261 C-261 D-261 E-260 F-261 G-261
Bolt-7 is South African, “Good”.
A-260 B-260 C-260 D-260 E-260 F-260 G-260
Note: Bolts 3/7 didn’t care which carrier they were in, same reading all seven. Bolts 1/2/6 varied in only one of seven carriers by .001. Now the carriers:

Carrier-A is StG/Austrian, “Excellent”, matches Bolt-1.
1-259 2-260 3-259 4-260 5-260 6-261 7-260
Carrier-B is StG/Belgian, “Very Good”, matches Bolt-2.
1-259 2-260 3-259 4-261 5-260 6-261 7-260
Carrier-C is South African, “Good”, matches Bolt-3.
1-259 2-260 3-259 4-261 5-261 6-261 7-260
Carrier-D is South African, “Good”, matches Bolt-4,
has high wear polish along bottom, the hammer from this kit also significantly burnished.
1-260 2-261 3-259 4-261 5-261 6-261 7-260
Carrier-E is South African, “Good”, matches Bolt-5.
1-259 2-260 3-259 4-260 5-260 6-260 7-260
Carrier-F is Belgian, “Excellent/New”, virtually no wear marks.
1-259 2-260 3-259 4-260 5-260 6-261 7-260
Carrier-G is South African, “Good”.
1-259 2-260 3-259 4-260 5-261 6-261 7-260
Note: Carriers A/B/F/G varied by .002, majority of readings in center. Carrier E varied by only .001, majority of readings at high end.

Conclusions: Exchanging bolts in particular carriers varied headspace by only .002, from .259 to .261, with the majority of the seven measuring .260. Exchanging carriers with particular bolts affected headspace even less, by only .001, and often not at all.

While this test included only seven of each component, they were of varied manufacture and condition. Obviously it would be better to have a larger sample, say 100 bolts/carriers, for more conclusive results, but based on the information gathered here it appears that, so long as you headspace towards the middle, swapping in spare bolts/carriers may be entirely practical. Of course, “your mileage may vary” and ALWAYS check headspace after swapping.


June 23, 2007, 14:10
Thanks Mosin Guy and Radio,

I had read some of those a while back (probably 2004 or 05). I was pretty sure metric/metric or inch/inch would work. I was suprised that the carriers would make a difference and that different bolts made so little difference (.002"). I didn't find a consensus on inch carriers with metric bolts. Radio's work was all with metric bolts and carriers. Ted made reference to them possibly not being reliable due to slight differences in camming angles, etc.

I may just get an inch carrier and bolt and try it. If it doesn't headspace correctly, try the inch carrier with my SA bolt. If that doesn't work build another. :smile:

June 23, 2007, 15:16
The standard admonition is to re-check headspace anytime you change a part that MIGHT affect headspace.

Once in a rare while, somebody will come along here and report a change in headspace of more than 0.001" as a consquence of changing carriers.

99% of the time you won't be able to tell one whit of difference after changing carriers. I would not hesitate to fire a FAL of known good headspace after only changing carriers.

I've done some mixing and matching with bolts and carriers on my guns, and I've never been able to detect more than 0.001" change.

If you want an inch-cut carrier, I say go right ahead.

June 23, 2007, 17:03
Like WEG says. The bolt/LS ensures proper headspace and changing the BC merely changes the bolts' method of transport. The purists/lawyers may argue for checking headspace whenever you change the BC solo or when changing the B with the BC as a set and checking headspace whenever you even clean the weapon (!) but I find it unnecessary.


June 23, 2007, 20:09
Rule #1. ALWAYS re-check the headspace after altering a component of the action.

Rule #2. Checking headspace is FUN!!!

Rule #3. Always embrace an opportunity to have FUN!!!


June 23, 2007, 20:46
I put a matching sand cut carrier and bolt in my favorite metric FAL which was a little on the loose side of headspace and it tightened it up a little.

Checking headspace is good for your head, face, hands and anything else that's tucked in close to that hunk of steel containing that explosion:wink:

June 23, 2007, 23:18
I agree checking headspace is fun. What I want to avoid is pressing out the locking shoulder, buying another one and pressing it back in. I asume the least number of times you do that the more likely the locking shoulder is to remain firmly in place. ;)

Thanks again guys :beer: :beer: :beer:

June 23, 2007, 23:19
Naturally. I would check the headspace too if I changed the B.


June 24, 2007, 00:18
Thanks Raspeguy. That was a great and detailed explanation! I hadn't considered the vertical play in the carrier or the verticle play between the bolt and carrier and what that would do to the bolts relationship with the locking shoulder.

June 24, 2007, 00:24
I am here to learn, thanks for the post. BUT. I just read the sticky at the top (British Amry Instructions) and it calls for the "Breech Block, removed from the carrier". Am I reading this incorrectly?


P.S. I just read Radio's post from 2003. Very interesting indeed. Thanks guys.

June 24, 2007, 09:28
I have read your post 5 or 6 times, it takes me a while before I "get it"!
A very interesting read, many thanks for the post.


June 24, 2007, 19:17
I want you to picture a stick being extended from behind a corner with my hat on it. I post this with great trepidation and caution, then I'm taking cover.

This is the core issue that surrounded the early Vanden Berg locking shoulders, being ground to a different angle than the much ballyhoo'ed "factory" angle. The difference in these angles caused a shortfall in headspace that surprised more than one builder. The angles do indeed matter.

The flames that surrounded this topic used to leap out of your computer screen around 2003/2004 and singe your eyebrows. It is a long-dead issue and all of Ed Vanden Berg's locking shoulders today are the cat's ass, perfect for any build... and I hesitatingly mention this issue ONLY in light of the current discussion regarding angles and headspace.

Retreat, retreat,