Can you measure the new bolt and compare against the old bolt dimensions and see if there is a difference? If they are the same dimensions I would try changing only the barrel at first. I would also call Sig and ask them what’s up. If it couldn’t verify dimensions I would follow your plan and still call Sig. Congrats on your new caliber exchange kit!
-
SigTalk is a forum community dedicated to SIG Sauer enthusiasts. Come join the discussion about Sig Sauer pistols and rifles, optics, hunting, gunsmithing, styles, reviews, accessories, classifieds, and more!
MCX barrel chages with or without bolt changes
In 2017 I bought an MCX Virtus in 300BLK . Today a new 16 inch barrel kit in 5.56 NATO is being delivered. The kit will contain a bolt. That bolt presumably has its headspace verified by SIG by one means or another to go with the new 5.56 barrel. The 300BLK barrel has a low round count due to ammo cost and the fact that I prefer my 9 inch MCX for 300BLK.
I'm going to change both the barrel and the bolt when the barrel arrives. (I will have the cost of a current Virtus single barrel setup in the two barrel setup which tells me how inflation has gone in guns.) The rub is that the process takes a bit more time to change both the barrel and bolt plus the barrel and bolt coming out needs to be kept together.
I already have a spare tapered bolt for the MCX series. Am I over thinking this by changing both the barrel and bolt or is SIG's silence in the manual on the matter wrong? SIG's video doesn't change the bolt with the barrel. By always including the bolt in a barrel kit it seems that SIG has given more than a hint.
Bill
I'm going to change both the barrel and the bolt when the barrel arrives. (I will have the cost of a current Virtus single barrel setup in the two barrel setup which tells me how inflation has gone in guns.) The rub is that the process takes a bit more time to change both the barrel and bolt plus the barrel and bolt coming out needs to be kept together.
I already have a spare tapered bolt for the MCX series. Am I over thinking this by changing both the barrel and bolt or is SIG's silence in the manual on the matter wrong? SIG's video doesn't change the bolt with the barrel. By always including the bolt in a barrel kit it seems that SIG has given more than a hint.
Bill
1 - 11 of 11 Posts
I don't have headspace gauges. Dimensions of the bolt are theoretically the same for SIG's MCX tapered bolts, i.e, the same part is used for both calibers.
Bill
Bill
My take on this is that the bolt was included for the people that still possess the legacy models. The legacy model don’t have the tapered lugs on the bolt and barrel extension like the Virtus models have. So instead of running the risk of damaging your firearm, they include the bolt to change both of them out. I do believe you are clear to only change the barrel since your bolt installed is the tapered type. Good luck with your exchange kit!In 2017 I bought an MCX Virtus in 300BLK . Today a new 16 inch barrel kit in 5.56 NATO is being delivered. The kit will contain a bolt. That bolt presumably has its headspace verified by SIG by one means or another to go with the new 5.56 barrel. The 300BLK barrel has a low round count due to ammo cost and the fact that I prefer my 9 inch MCX for 300BLK.
I'm going to change both the barrel and the bolt when the barrel arrives. (I will have the cost of a current Virtus single barrel setup in the two barrel setup which tells me how inflation has gone in guns.) The rub is that the process takes a bit more time to change both the barrel and bolt plus the barrel and bolt coming out needs to be kept together.
I already have a spare tapered bolt for the MCX series. Am I over thinking this by changing both the barrel and bolt or is SIG's silence in the manual on the matter wrong? SIG's video doesn't change the bolt with the barrel. By always including the bolt in a barrel kit it seems that SIG has given more than a hint.
Bill
That makes a lot of sense. 👍🏻My take on this is that the bolt was included for the people that still possess the legacy models. The legacy model don’t have the tapered lugs on the bolt and barrel extension like the Virtus models have. So instead of running the risk of damaging your firearm, they include the bolt to change both of them out. I do believe you are clear to only change the barrel since your bolt installed is the tapered type. Good luck with your exchange kit!
You make a very good point about the tapered bolt and the generational bolt differences. However, headspace is a critical safety issue. Also, wear in is an issue with two different barrel extensions. The reason I'm changing bolts is to let the bolt and barrel mate together and hopefully run more smoothly.My take on this is that the bolt was included for the people that still possess the legacy models. The legacy model don’t have the tapered lugs on the bolt and barrel extension like the Virtus models have. So instead of running the risk of damaging your firearm, they include the bolt to change both of them out. I do believe you are clear to only change the barrel since your bolt installed is the tapered type. Good luck with your exchange kit!
Bill
MCX head spacing's a good question. SIG only started shipping bolts with Virtus taper barrel kits, so my impression is it's SIG's assurance their new taper barrel kits will run in their previous MCX versions.
I've run our MCX Legacy with about the same round counts in 300Blk & 5.56 with a mix of both legacy and taper bolts. 300Blk were 16", 9" and 6.75" barrels with legacy bolt setups, and 5.56 were 16" barrel with legacy bolt and 11.5" barrel with Virtus' taper bolt. No failures or cycling problems with any of these setups.
I have a vague memory of something in '15 about SIG MCX's headspace mgmt, but don't recall specifics..
Cheers
I've run our MCX Legacy with about the same round counts in 300Blk & 5.56 with a mix of both legacy and taper bolts. 300Blk were 16", 9" and 6.75" barrels with legacy bolt setups, and 5.56 were 16" barrel with legacy bolt and 11.5" barrel with Virtus' taper bolt. No failures or cycling problems with any of these setups.
I have a vague memory of something in '15 about SIG MCX's headspace mgmt, but don't recall specifics..
Cheers
I've bought exchange kits without bolts.
You can buy bolts separately.
I understand the importance of head spacing but I figure if it's an issue, sig would always pair barrel/bolt and would have spread the word more.
Honest questions: Has there been a head space issue with the MCX? That wasn't a one off? Virtus or legacy? Does sig take the time to match bolt and barrel?
You can buy bolts separately.
I understand the importance of head spacing but I figure if it's an issue, sig would always pair barrel/bolt and would have spread the word more.
Honest questions: Has there been a head space issue with the MCX? That wasn't a one off? Virtus or legacy? Does sig take the time to match bolt and barrel?
The only reason I have for concern on head space with a barrel change is tolerance stack up when there is a five year gap in manufacturing between the new barrel and the original bolt with the original upper. I'm going with keeping the new barrel and bolt pair together.
Bill
Bill
Well, today was range day for two MCXs in 5.56. There was a bit of a downpour so the outdoor range was deserted, perhaps due to the flood warning and the club being right on the Spokane river.
Both MCX Verti were flawless. Groups were held to an inch at 50 yards during the downpour on the two new barrels. There were no signs of excess pressure. So SIG's head spacing was fine.
Bill
Both MCX Verti were flawless. Groups were held to an inch at 50 yards during the downpour on the two new barrels. There were no signs of excess pressure. So SIG's head spacing was fine.
Bill
After doing some reading on aluminum billets versus forgings, I have concluded that SIG likely used 6061 billets to make MCXs due to the requirements for precision machining on the MCX. The precision machining supports the ability to do barrel swaps while maintaining precision head spacing. The 6061 aluminum billets vs 7075 also reduce the cost of keeping very precise cutting tools sharp.
I also suspect that the tapered bolts in the Virtus generation help maintain head spacing in addition to increasing bolt life. SIG has also gone to polymer coatings in the MCX Virtus uppers to reduce wear and perhaps to keep up with HK. Some of the recent MCX related postings lead me to believe that it's very important for MCXs to be well lubed to maintain various tolerances.
Bill
I also suspect that the tapered bolts in the Virtus generation help maintain head spacing in addition to increasing bolt life. SIG has also gone to polymer coatings in the MCX Virtus uppers to reduce wear and perhaps to keep up with HK. Some of the recent MCX related postings lead me to believe that it's very important for MCXs to be well lubed to maintain various tolerances.
Bill
1 - 11 of 11 Posts
- This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
SIG Talk
A forum community dedicated to SIG Sauer Pistols and SIG Sauer Rifles owners and enthusiasts. Come join the discussion about optics, hunting, gunsmithing, styles, reviews, accessories, classifieds, and more!
Full Forum Listing
Explore Our Forums
Top Contributors this Month
View All
Harry_Gorilla
787 Replies
cremaley
724 Replies
dwg13013
307 Replies
