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2/3/2025 10:29:29 PM EDT
So I have been testing this gun aggressively the last month or so in the cold below are the rifle specs

10” scar 16
Cherry bomb muzzle device
.063 gas jet
Brownells fde aluminum magazine
Nrch bolt
800 rounds on the gun

My test goes as follows:

Take the gun outside, 5 rounds in the mag load it out it on the back porch over night, fire the next morning, the gun is cleaned before each oil test 100% stripped and cleaned
So far no oil is any better than the other.

I’ll fire a round or 2 and the gun will cycle but then the bolt will only go 3/4 of the way home or I’ll pull the trigger and get the dead man’s click.

So the other night I polished the following parts:

Cam pin
Firing pin
Bolt head and bolt head body
Channel the cam pin rides in
Chamber

I need to shoot it but did a manual function check and seemed good actually a bit smoother, I might send out a few parts for dlc and nitride.

Fn guy said the nrch bolt is much lighter and suggested a rch bolt instead but idk if it will work in the nrch receiver, he also told me what I was doing was pretty dumb, but I told him that I do a lot of winter day and night shoots and I cannot have it fail during a class so ???????

Any suggestions ? Possibly drag on the sled ?
2/4/2025 7:04:36 AM EDT
[#1]
Have you tried incrementally increasing the gas jet?
2/4/2025 8:45:41 AM EDT
[#2]
What oil? They matter.

What temps?
2/4/2025 9:14:28 AM EDT
[Last Edit: fxntime][Edited] [#3]
You need a light oil carrier that evaporates and leaves behind a thin film of silicone/teflon/graphite to do the lubing. Put your oils in the freezer and see how much they thicken up in the cold. Maybe try a 0W-15 motor oil over some ''great gun oil'' that doesn't really get temp tested like most motor oils do. I think basically all low viscosity motor oils are synthetic because ''dino'' oil can't make the low viscosity grades.

Maybe try some Silikroil, thin but has silicone for lubricating properties. You need to stay away from anything that starts to gum and stick when it gets cold.
Liberals are a curious mix of communism and fascism, they want to destroy you but want to use your own money to do it.

I'm getting down to the last box, the others have all been destroyed...
2/4/2025 9:24:09 AM EDT
[#4]
Specifically G96 gun oil has worked for me in the past.
2/4/2025 9:42:14 AM EDT
[#5]
Quote History
Originally Posted By CJofFL:
Have you tried incrementally increasing the gas jet?
View Quote



No only because I don’t have issues with cycling outside of freezing the gun, it’s possible it could be the gas but the gun hangs up when it’s returning to battery, but I can put the factory one back in 🤷🏻‍♂️
2/4/2025 9:43:19 AM EDT
[#6]
Quote History
Originally Posted By dalyman72:
What oil? They matter.

What temps?
View Quote


M-pro7 lxp,  14-25 degrees
2/4/2025 9:45:00 AM EDT
[#7]
Quote History
Originally Posted By fxntime:
You need a light oil carrier that evaporates and leaves behind a thin film of silicone/teflon/graphite to do the lubing. Put your oils in the freezer and see how much they thicken up in the cold. Maybe try a 0W-15 motor oil over some ''great gun oil'' that doesn't really get temp tested like most motor oils do. I think basically all low viscosity motor oils are synthetic because ''dino'' oil can't make the low viscosity grades.

Maybe try some Silikroil, thin but has silicone for lubricating properties. You need to stay away from anything that starts to gum and stick when it gets cold.
View Quote



Using mpro7 lxp oil, I think it has a -65 or -85 rating, my temps I am testing In is between 10 and 23 degrees
2/4/2025 9:48:48 AM EDT
[#8]
Quote History
Originally Posted By Small_white_D:



Using mpro7 lxp oil, I think it has a -65 or -85 rating, my temps I am testing In is between 10 and 23 degrees
View Quote View All Quotes
View All Quotes
Quote History
Originally Posted By Small_white_D:
Originally Posted By fxntime:
You need a light oil carrier that evaporates and leaves behind a thin film of silicone/teflon/graphite to do the lubing. Put your oils in the freezer and see how much they thicken up in the cold. Maybe try a 0W-15 motor oil over some ''great gun oil'' that doesn't really get temp tested like most motor oils do. I think basically all low viscosity motor oils are synthetic because ''dino'' oil can't make the low viscosity grades.

Maybe try some Silikroil, thin but has silicone for lubricating properties. You need to stay away from anything that starts to gum and stick when it gets cold.



Using mpro7 lxp oil, I think it has a -65 or -85 rating, my temps I am testing In is between 10 and 23 degrees


It may lube still but it may still be too thick. That is why I said try the freezer and see how much it thickens. Use a small container like a OTC pill bottle.
Liberals are a curious mix of communism and fascism, they want to destroy you but want to use your own money to do it.

I'm getting down to the last box, the others have all been destroyed...
2/4/2025 11:32:36 AM EDT
[#9]
Quote History
Originally Posted By fxntime:


It may lube still but it may still be too thick. That is why I said try the freezer and see how much it thickens. Use a small container like a OTC pill bottle.
View Quote


This oil is super thin, almost like water thin
2/4/2025 11:52:38 AM EDT
[#10]
Quote History
Originally Posted By Small_white_D:



No only because I don’t have issues with cycling outside of freezing the gun, it’s possible it could be the gas but the gun hangs up when it’s returning to battery, but I can put the factory one back in 🤷🏻‍♂️
View Quote

Start there. Lubricant is probably not the issue
2/4/2025 1:08:57 PM EDT
[Last Edit: CJofFL][Edited] [#11]
Quote History
Originally Posted By Small_white_D:No only because I don’t have issues with cycling outside of freezing the gun, it’s possible it could be the gas but the gun hangs up when it’s returning to battery, but I can put the factory one back in 🤷🏻‍♂️
View Quote
Stock gas port for a 10" is 2.1mm. Mine would only lock on a 1.50mm or more as seen here... https://www.ar15.com/forums/Armory/Scar-16-factory-10-unsuppressed-AE-223-gas-port-size/24-550797/ So, you may be near the minimum for reliable functioning regardless and the cold weather may be pushing it over the edge.
2/4/2025 1:13:43 PM EDT
[Last Edit: Zerlak][Edited] [#12]
Quote History
Originally Posted By Small_white_D:



No only because I don’t have issues with cycling outside of freezing the gun, it’s possible it could be the gas but the gun hangs up when it’s returning to battery, but I can put the factory one back in 🤷🏻‍♂️
View Quote View All Quotes
View All Quotes
Quote History
Originally Posted By Small_white_D:
Originally Posted By CJofFL:
Have you tried incrementally increasing the gas jet?



No only because I don’t have issues with cycling outside of freezing the gun, it’s possible it could be the gas but the gun hangs up when it’s returning to battery, but I can put the factory one back in 🤷🏻‍♂️


Working fine in mild temps isn't the same as working fine in extreme temps. Betting your SCAR would function fine with the factory gas jet and your test.
2/4/2025 2:38:49 PM EDT
[#13]
Quote History
Originally Posted By Zerlak:


Working fine in mild temps isn't the same as working fine in extreme temps. Betting your SCAR would function fine with the factory gas jet and your test.
View Quote



I can go back to it and try
2/4/2025 2:45:44 PM EDT
[#14]
Quote History
Originally Posted By CJofFL:
Stock gas port for a 10" is 2.1mm. Mine would only lock on a 1.50mm or more as seen here... https://www.ar15.com/forums/Armory/Scar-16-factory-10-unsuppressed-AE-223-gas-port-size/24-550797/ So, you may be near the minimum for reliable functioning regardless and the cold weather may be pushing it over the edge.
View Quote



Interesting mine came with a 1.2mm gas jet
2/4/2025 7:38:23 PM EDT
[#15]
Quote History
Originally Posted By Small_white_D: Interesting mine came with a 1.2mm gas jet
View Quote
That certainly wouldn’t cycle mine.
2/5/2025 3:39:28 AM EDT
[#16]
Sending my bolt and cam pin and extractor and piston and sled (nrch) out for nitride and tonight I polished inside my trunion and in my chamber and barrel face
2/5/2025 7:09:54 AM EDT
[#17]
I had this issue with my 10" scar 16 after I put a smaller gas jet into it. I don't remember the specific size, but I got it all configured and working but it was the summer. I took it out in the Utah winter and it just short stroked every round.

I haven't yet, but I'm planning to get one of the adjustable gas components like the Scarburator or whatever and then just leave the stock gas jet in and dial it down when it's warm.
2/5/2025 7:40:07 PM EDT
[#18]
https://www.parkermountainmachine.com/product/pmm-scar-1617-stainless-steel-gas-jets/

FACTORY SCAR 16



16″: 1.35MM

14″: 1.45MM

10″: 2.00MM



FACTORY SCAR 17



16″: 1.45MM

13″: 1.60MM
2/5/2025 10:25:53 PM EDT
[Last Edit: CJofFL][Edited] [#19]
Quote History
Originally Posted By stevelish: FACTORY SCAR 16… 10″: 2.00MM
View Quote
Yeah, something doesn’t sound right about the 1.2mm size the OP mentioned. I measured my factory 10” at 2.1mm with a pin gauge.
2/6/2025 3:55:22 AM EDT
[#20]
Quote History
Originally Posted By stevelish:
https://www.parkermountainmachine.com/product/pmm-scar-1617-stainless-steel-gas-jets/

FACTORY SCAR 16



16″: 1.35MM

14″: 1.45MM

10″: 2.00MM



FACTORY SCAR 17



16″: 1.45MM

13″: 1.60MM
View Quote


I am using a 1.9 in my scar
2/6/2025 5:58:19 AM EDT
[#21]
Quote History
Originally Posted By Small_white_D:


I am using a 1.9 in my scar
View Quote
Why did you change out the factory gas jet?

You're saying the factory was 1.2, so you changed it out for a 1.9?

Does that mean it simply wouldn't cycle from the factory, so you sought out a larger gas jet?


2/6/2025 7:39:13 AM EDT
[#22]
Quote History
Originally Posted By Daggertt: You're saying the factory was 1.2, so you changed it out for a 1.9?
View Quote
And the OP says 1.6mm, so gas jet changes need clarification and context.
2/6/2025 9:57:05 AM EDT
[#23]
Quote History
Originally Posted By Daggertt:
Why did you change out the factory gas jet?

You're saying the factory was 1.2, so you changed it out for a 1.9?

Does that mean it simply wouldn't cycle from the factory, so you sought out a larger gas jet?


View Quote


Yes, when I got my 10” barrel it would not cycle, I did some research and started making my own gas jets, I am a machinist so I got a list of the jet sizes  and made a set, starting from 2mm I tried them all then found the one that shot reliable and soft with out my suppressor on
2/6/2025 11:40:08 AM EDT
[#24]
Quote History
Originally Posted By Small_white_D:


Yes, when I got my 10" barrel it would not cycle, I did some research and started making my own gas jets, I am a machinist so I got a list of the jet sizes  and made a set, starting from 2mm I tried them all then found the one that shot reliable and soft with out my suppressor on
View Quote
did you get your 10" barrel factory new or had a previous owner already been messing with gas jets in it?
2/14/2025 9:40:59 PM EDT
[#25]
Do not nitride any parts

Use the factory size gas jet for a 10" barrel

Use either: a. Slip 2000 EWL over all moving parts and inside of the barrel
               b. A heavy weight motor oil like OW-20 or OW-30 Mobil 1 synthetic over all moving parts (be careful, it is toxic)

Those two oils appear to work the best in cold weather tests.

https://youtu.be/ne-AgWDbVns?si=YBfJAZiJTXpKgdyN
Elite Soviet Democrat
3/28/2025 7:08:08 PM EDT
[#26]
I don't know if it were mentioned, but it's probably your ammo temp. Run that same test with 5 rounds that are 72* from indoors and I bet it works.

After that, it's 100% your reduced gas jet.

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