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Chaszel 20 Gauge to 357 Shotgun Adapter 18"

357 Mag 20 Gauge Shotgun Adapters

(12 customer reviews)


357 Magnum Shotgun Adapters for 20 Gauge Shotguns

Adapters come in 4 Lengths

2 3/4″ 5″, 11″ and 18″

All Adapters are Fully Rifled with a 1-12 or 1-18″ Twist.

Select Length below: 


357 Mag Shotgun Adapters for 20 Gauge Shotguns

357 Mag Shotgun Adapters Allow a 20 Gauge Break Action Shotgun to use 357 Magnum or 38 Special Ammo.

For 3″ as well as 2.75″ Chambers

Compatible with Break Action single as well as double barrel shotgun.

Comes with multiple O-ring configurations.  As a result,  easily achieving a good fit for 20 gauge shotguns.

Rifle dimensions are .355″/.349″ with 6 lands and .125″ wide.

Black Oxide coating as a result provides notably better corrosion protection (for maximum corrosion protection keep a thin coat of oil on the insert)

Please Note:  Not all shotguns are the same!  While the majority of them are capable of handling high pressure rounds, some are NOT.  Only use these rounds in shotguns that are compatible.  I recommend on any shotgun to test the first shot in a vice while out of harms way and to always wear eye and ear protection.  If after testing you see the primer punctured in the round discontinue using this round and use a less powerful round. These high pressure rounds include: 45-70 gov., 357 Mag Shotgun Adapters, 327 Federal, 44 Mag, and 22 Hornet.  Please always be safe and aware.
Thank you for reading.

What are Shotgun Adapters?

Shotgun Adapters frequently called Chamber Reducers or Shotgun Barrel Inserts. Our shotgun adapters allow you to use other types of ammunition in a Break Action Shotgun. Including double barrel and over and under double barrels in addition to the popular single barrel break action. We offer several different versions to suit your preference in ammunition, as well as length. 12 and 20 Gauge shotgun adapters are our most popular adapters followed closely by the 410. 16 Gauge is something we plan on expanding in the future.


However, not all shotguns are capable of handling all of the shotgun adapters we offer. Low-pressure rounds work in any shotgun, whereas high-pressure rounds can cause problems in some shotguns. The problem is when the firing pin punctures the primer. This event causes the gases to escape and possibly damage the firing pin. All adapters chambered for high-pressure rounds have red text on the website, signifying that is is a high-pressure round. These adapters also include a pamphlet with more information about this concept. In addition These Shotgun Adapters also have a Low-Preasure round alternative.


357 Mag Shotgun Adapters

Most of our shotgun adapters come in different lengths to suit your needs. Some like the secure storage and portably of Shell length adapters. Whereas some are looking to get the most fps (feet per second) or accuracy out of their adapter. Black Oxide has become our standard finish. We can offer unfinished adapters during our production if you have requested one.

FPS (Feet Per Second)

As a general rule, the longer the adapter, the more FPS it produces. However, with low-pressure rounds such as the 45 colt, the fps difference is minimal once past the 11″ length. If you are interested, here is an excellent website that gives a good idea of fps per inch BBTI. All of our shotgun adapters are entirely made in the United States and are an affordable addition to your break action shotgun. Thank you for you interest in our Shotgun Adapters or Chamber Reducers. We are working to make more adapters for more calibers, so you can sign up to be notified here
The video below gives a brief demonstration of how they work.

We are working to make more adapters for more calibers, so you can sign up to be notified here. Thank you for your interest.

If you like this product, check out our other Shotgun Adapters

Additional information


2 3/4", 5", 11, 18"


Black Oxide, No Finish (Silver)

12 reviews for 357 Mag 20 Gauge Shotgun Adapters

  1. Riley (verified owner)

    I purchased a 357 Mag 20 gauge adapter and this product really exceeded my expectations. I wanted an 18 inch adapter, but that wasn’t available. The 11 inch adapter was and it is excellent. I set up a target at 55-60 yards (the area around the 50 yard mark was muddier than normal), I put four shots within a 6 inch circle on the paper. I need to practice more and I’m sure accuracy will go up. I moved the target to 100 yards. At 100 yards, it should be known I have a Stoeger Conder 20 ga O/U. So in terms of bead placement, the bead covered the entire target. My first shot was a flyer as it was high and right. The last three shots were more or less just outside a 6 inch target. It was all to the right, but I was using a bead, not rifled sights. The 11 inch insert went 8/8 for shots on paper, it is consistent and easy to use. I know changing sights will make an impact and I will explore some of those. I can’t wait for more caliber to come out! I plan on using this for deer season this fall, I just need to practice more first.

  2. steve (verified owner)

    excellent workmanship

  3. Dean Santomango (verified owner)

    Excellent quality

  4. Anonymous (verified owner)

  5. John (verified owner)

  6. Anonymous (verified owner)

    Quick delivery and on checking up the adapter, the machining looks excellent.
    I did put a note in the Graybeard forum about the product.

    • Chaszel (store manager)

      Thank you for your product Review, We really appreciate it.


  7. James Ballou (verified owner)

    Chaszel makes a super high-quality, well designed and finely machined product, they mail the orders right away, their prices for these types of products simply cannot be beat, and in my experience their customer service is outstanding.

  8. Amanda McGowan (verified owner)

    I could not be more pleased with this product. It has breathed new life into my topper jr. I plan on purchasing more calibers when they are available.

  9. Mark Wilson (verified owner)

    quick reply, i like the interaction, overall great experience, would recommend again

  10. Jeremiah wimmer (verified owner)

    Awesome product works amazing it is as they said

  11. Troy D. (verified owner)

    I have not used the 357 insert yet, the bore for the bullet casing seems a little large. mic’d at .3805. Measurements on the 357 cartridges I have are .3755 so have a little play when placed in the insert. Bore is correct and the lands and grooves look great..

    • Chaszel (store manager)

      The loose fit is normal. Saami specifications call for .381″ at the opening. If you have any other concerns or questions feel free to let me know. Thank you very much for your business and your feedback.


  12. Corey W. (verified owner)

    Sent me the wrong one. When I emailed them they immediately returned my email and sent me the correct one. Great product and great customer service.

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