Comparison of 180 and 181 (and later) series - Shooting Sports Forum


Ruger Mini-14 and Mini-30 Ruger Mini-14 and Mini-30 family of rifles

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Old 12-19-2019, 13:31   #1
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Comparison of 180 and 181 (and later) series

I've always wondered exactly what was different between the 180 series Mini 14s and the later 181-197 series Mini 14s. This morning I took them apart and made a detailed comparison.

The most obvious external change is the bolt hold open arrangement, but that's actually mostly cosmetic, although I do think that the older 180 series arrangement is more functional. You can pull the bolt back with your index finger and then reach around the heel of the receiver and press the bolt hold open down. The slide release also has has enough leverage to release the bolt even against magazine follower pressure.



I discovered the major change is in the slide/operating rod, and that drives most of the other parts changes in the later Mini 14s.



The operating rod on the 180 series weighs 303 grams while the 181 series slide/operating rod weighs 382 grams. The 181 slide/operating rod is noticeably deeper in the belly, which is where the additional weight is located. That deeper profile then is what requires the deeper profile on the 181 stock's forened, and in turn it requires the bottom half of the gas block assembly to be longer.



There are some detail changes to the shape of the gas pipe, but the diameter and length are the same. The top piece of the gas block assembly appears to be identical in the 180 and 181. The recoil spring guide rod is slightly larger in diameter in the 181 series, and in turn so is the recoil spring and the hole in the slide/operating rod for the spring. The gas port bushing on the 180 series is about .063" in diameter, considerably smaller than the .080" in the 181 series.



In short, Ruger made the 181 series slide/operating rod heavier, installed a slightly heavier guide rod and a larger internal diameter spring and fed it a bit more gas.

The front tangs on the 181 receiver are consequently slightly longer to accommodate the deeper belly on the slide/operating rod, and the receiver is arguably a bit stronger in this area.



Interestingly, the slide/operating rods are otherwise interchangeable. Theoretically, if you broke the slide/operating rod in a 180 series Mini 14, you could use a 181 operating rod, provided you put the rifle in a 181 series stock, along with the lower half of a 181 series gas block, and switched the recoil spring guide rod and spring for 181 series parts to manage the additional reciprocating weight. The 180's .063" gas port bushing should be fine.

Similarly, if you owned a 180 series Mini 14 it could be used in a 181 series (or later) stock, if you also change the lower half of the gas block assembly to match the deeper stock profile. There would just be more clearance for the smaller 180 slide/operating rod inside the stock. There would be some room under the front tangs, but it would not be significant.

Swapped slide/operating rods:



The stock liners are identical. The 180 liner is used in the 181 series, it just doesn't go all the sway up the sides of the stock, and the resulting gap in the 181 stock, shows the increase in depth of the stock.





The same is true at the receiver. The forward tab on the 181 insert was simply shortened slightly to connect with the now lower stock liner in the deeper stock. Consequently, the front tab on a 181 series insert could be bent and shortened to fit the 180 series.




The bolts are obviously different in that the 180 has a roller and the 181 series just has a round lug - that is shaped just like the roller. There is some minor differences in the extractor but the bolt face, cut for the ejector, and the lug arrangement and dimensions, and length and firing pin arrangements are identical. The major difference is that the tip on the back of the bolt is higher on the 181 series, and there is a bit more meat in the back of the 181 series bolt.




It would take a little work, but the rear portion of a 181 series bolt could be filed down to fit a 180 series rifle. Head spacing would however be a large question mark. Too little is an easy fix. To much would require setting the barrel back and that would quickly snowball (gas port and gas block location, etc). Fortunately bolts don't seem to break and Jack First makes improved 180 extractors so that won't make a 180 bolt unusable.

In addition to the longer forward tangs on the 181 receiver, the receivers are different in terms of the bolt stop arrangement. But the bolt stop related differences are all above the stock line and don't affect the fit of a stock in that area. One of the big rumors is that the 180's receiver is longer. It's not. Maybe that's a confusion with the longer heel on the AC556 to accommodate the fire selector.

I could find no differences at all in the trigger groups, and they are interchangeable on the two rifles.
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Old 12-19-2019, 16:03   #2
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A stunningly detailed post with the differences......much thanks
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Old 12-19-2019, 16:27   #3
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Very nice work!

Question: Are the top wood hand-guards interchangeable between the 180 and 181?
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Old 12-19-2019, 18:22   #4
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Originally Posted by Beck View Post
Very nice work!

Question: Are the top wood hand-guards interchangeable between the 180 and 181?
I haven't tried it, but the top half of the gas block is the same, the length from receiver to gas block is the same, and the barrel profile is the same, so the 181 handguard should fit a 180 series rifle. The 180 handguard however will not fit a 181 barrel as it lacks the grooves milled in the barrel to accommodate the Garand/M14 style metal clip.
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Old 12-20-2019, 07:49   #5
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Thumbs up

This is one of those “now I know” things that enhances our understanding and body of knowledge. Thank you for the succinct lesson. Test on Monday!
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Old 12-22-2019, 08:36   #6
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Thanks for the comparison!
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Old 12-23-2019, 15:16   #7
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Amen thanks for the comparison write up and pics. Hats off to you sir!
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Old 12-27-2019, 03:27   #8
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Some very interesting differences that I didn’t know about.
Appreciate all the pics and the detailed differences.
Much thanks
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Old 02-29-2020, 04:29   #9
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Excellant post, my only mini is a 1976 made model 180. Good info to know.
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Old 02-29-2020, 04:39   #10
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Originally Posted by Beck View Post
Very nice work!

Question: Are the top wood hand-guards interchangeable between the 180 and 181?

Yes, they are. Some years ago I had a wood hand guard on a 182- Mini
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Old 02-29-2020, 09:06   #11
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Great Job!
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Old 03-01-2020, 23:50   #12
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Thanks for the write up
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Old 03-02-2020, 21:14   #13
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Originally Posted by Bender View Post
Yes, they are. Some years ago I had a wood hand guard on a 182- Mini
Not quite. See post #4.
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Old 03-03-2020, 20:46   #14
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183 also came with the wood upper guard.
Thanks for the info great stuff.
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